gallium: Add buffer and configs handling or fp16 formats

Expose configs when allow_fp16_configs has been enabled and
DRI_LOADER_CAP_FP16 is set in the loader.

Also, make kms_swrast_dri respect format bpp, to allow for allocating
buffers wider than 32 bpp.

Make fp16 opt-in for gallium.

Signed-off-by: Kevin Strasser <kevin.strasser@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
22 jobs for !794 with fp16-v2 in 24 minutes and 5 seconds (queued for 53 seconds)
latest detached
Status Job ID Name Coverage
  Containers Build
passed #523085
debian

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  Build+Test
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meson-arm64

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passed #523093
meson-armhf

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passed #523087
meson-clang

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meson-clover

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meson-i386

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passed #523090
meson-main

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passed #523086
meson-swr-glvnd

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passed #523092
meson-vulkan

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passed #523097
scons-llvm

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passed #523096
scons-nollvm

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passed #523088
scons-swr

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passed #523089
scons-win64

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  Test
passed #523098
test-llvmpipe-gles2 1/4

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passed #523099
test-llvmpipe-gles2 2/4

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passed #523100
test-llvmpipe-gles2 3/4

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passed #523101
test-llvmpipe-gles2 4/4

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passed #523102
test-softpipe-gles2 1/4

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passed #523103
test-softpipe-gles2 2/4

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passed #523104
test-softpipe-gles2 3/4

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passed #523105
test-softpipe-gles2 4/4

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passed #523106
test-softpipe-gles3-limited

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