glx: Only allow one DRI backend per display

This could only have been useful if you had multiple screens, each
needing different DRI backends, and you were trying to talk to them all
from a single process. I am unconvinced that this is a thing to care
about.
108 jobs for !8013 with glx-one-dri-backend in 11 seconds (queued for 4 seconds)
latest detached
Status Job ID Name Coverage
  Sanity
passed #7700301
sanity

00:00:11

 
  Container
manual #7700307
aarch64 manual
arm_build
manual #7700310
manual
arm_test-base
manual #7700311
windows shell 1809 mesa manual
windows_build_vs2019
manual #7700303
manual
x86_build-base
manual #7700305
manual
x86_test-base
 
  Container 2
created #7700329
android_build
created #7700336
arm64_test
created #7700338
armhf_test
created #7700323
i386_build
created #7700314
kernel+rootfs_amd64
created #7700317
aarch64
kernel+rootfs_arm64
created #7700319
aarch64
kernel+rootfs_armhf
created #7700325
ppc64el_build
created #7700327
s390x_build
created #7700321
x86_build
created #7700332
x86_test-gl
created #7700334
x86_test-vk
 
  Meson X86 64
created #7700347
meson-clang
created #7700348
meson-clover
created #7700344
meson-clover-testing
created #7700345
gstreamer
meson-gallium
created #7700346
meson-release
created #7700341
meson-testing
created #7700342
meson-testing-asan
created #7700349
meson-vulkan
 
  Build Misc
created #7700350
meson-android
created #7700352
aarch64
meson-arm64
created #7700353
aarch64
meson-arm64-asan
created #7700354
aarch64
meson-arm64-build-test
created #7700351
aarch64
meson-armhf
created #7700356
meson-i386
created #7700359
meson-mingw32-x86_64
created #7700358
kvm
meson-ppc64el
created #7700357
kvm
meson-s390x
created #7700355
windows docker 1809 mesa
meson-windows-vs2019
 
  Amd
created #7700360
mesa-ci-aarch64-lava-collabora
radeonsi-stoney-gles31:amd64
created #7700361
mesa-ci-aarch64-lava-collabora
radeonsi-stoney-traces:amd64
created #7700362
radv-fossils
 
  Arm
created #7700368
mesa-ci-aarch64-lava-collabora
panfrost-g52-gles2:arm64
created #7700369
mesa-ci-aarch64-lava-collabora
panfrost-g52-gles3:arm64
created #7700363
mesa-ci-aarch64-lava-collabora
panfrost-t720-gles2:arm64
created #7700364
mesa-ci-aarch64-lava-collabora
panfrost-t860-gles2:arm64
created #7700365
mesa-ci-aarch64-lava-collabora
panfrost-t860-gles3:arm64 1/2
created #7700366
mesa-ci-aarch64-lava-collabora
panfrost-t860-gles3:arm64 2/2
created #7700367
mesa-ci-aarch64-lava-collabora
panfrost-t860-traces:arm64
 
  Broadcom
created #7700380
igalia-rpi4
v3d-rpi4-gles2:armhf
created #7700374
igalia-rpi4
v3d-rpi4-gles31:armhf 1/2
created #7700375
igalia-rpi4
v3d-rpi4-gles31:armhf 2/2
created #7700376
igalia-rpi4
v3d-rpi4-gles3:armhf 1/4
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igalia-rpi4
v3d-rpi4-gles3:armhf 2/4
created #7700378
igalia-rpi4
v3d-rpi4-gles3:armhf 3/4
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igalia-rpi4
v3d-rpi4-gles3:armhf 4/4
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igalia-rpi4
v3dv-rpi4-vk:armhf 1/6
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igalia-rpi4
v3dv-rpi4-vk:armhf 2/6
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igalia-rpi4
v3dv-rpi4-vk:armhf 3/6
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igalia-rpi4
v3dv-rpi4-vk:armhf 4/6
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igalia-rpi4
v3dv-rpi4-vk:armhf 5/6
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igalia-rpi4
v3dv-rpi4-vk:armhf 6/6
created #7700370
igalia-rpi3
vc4-rpi3-gles2:armhf 1/4
created #7700371
igalia-rpi3
vc4-rpi3-gles2:armhf 2/4
created #7700372
igalia-rpi3
vc4-rpi3-gles2:armhf 3/4
created #7700373
igalia-rpi3
vc4-rpi3-gles2:armhf 4/4
 
  Freedreno
created #7700387
google-freedreno-db410c
a306_gles2
created #7700388
google-freedreno-db410c
a306_gles3 1/3
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google-freedreno-db410c
a306_gles3 2/3
created #7700390
google-freedreno-db410c
a306_gles3 3/3
created #7700391
google-freedreno-db410c
a306_gles3_options
created #7700392
google-freedreno-db820c
a530_gles2 1/2
created #7700393
google-freedreno-db820c
a530_gles2 2/2
created #7700394
google-freedreno-db820c
a530_gles3
created #7700395
google-freedreno-db820c
a530_gles31
created #7700399
google-freedreno-cheza
a630_gl
created #7700396
google-freedreno-cheza
a630_gles2
created #7700398
google-freedreno-cheza
a630_gles3
created #7700397
google-freedreno-cheza
a630_gles31
created #7700401
google-freedreno-cheza
a630_gles_asan
created #7700400
google-freedreno-cheza
a630_gles_others
created #7700405
google-freedreno-cheza
a630-traces
created #7700402
google-freedreno-cheza
a630_vk 1/2
created #7700403
google-freedreno-cheza
a630_vk 2/2
created #7700404
google-freedreno-cheza
a630_vk_sysmem
 
  Software Renderer
created #7700411
lavapipe-vk
created #7700410
llvmpipe-gles2
created #7700407
llvmpipe-piglit-glslparser
created #7700406
llvmpipe-piglit-quick_gl
created #7700408
llvmpipe-piglit-quick_shader
created #7700409
llvmpipe-traces
created #7700416
softpipe-asan-gles31
created #7700418
softpipe-gl
created #7700412
softpipe-gles2
created #7700413
softpipe-gles3
created #7700414
softpipe-gles31 1/2
created #7700415
softpipe-gles31 2/2
created #7700417
softpipe-piglit-quick
 
  Layered Backends
created #7700431
windows docker 1809 mesa
test-d3d12-windows
created #7700423
virgl-gl30-on-gl
created #7700424
virgl-gl31-on-gl
created #7700425
virgl-gl32-on-gl
created #7700419
virgl-gles2-on-gl
created #7700421
virgl-gles31-on-gl 1/2
created #7700422
virgl-gles31-on-gl 2/2
created #7700420
virgl-gles3-on-gl
created #7700426
virgl-traces
created #7700430
zink-lvp-gl
created #7700428
zink-lvp-gles2
created #7700429
zink-lvp-gles3
created #7700427
zink-piglit-quick_gl