lavapipe: add single ssbo variable pointer support.

Multiple buffer seems to break with tess eval only,
something to investigate later.
50 jobs for !8222 with lavapipe-var-pointer in 10 seconds (queued for 6 seconds)
detached
Status Job ID Name Coverage
  Sanity
passed #7005748
sanity

00:00:10

 
  Container
manual #7005752
aarch64 manual
arm_build
manual #7005754
manual
arm_test-base
manual #7005756
windows shell 1809 mesa manual
windows_build_vs2019
manual #7005750
manual
x86_build-base
manual #7005751
manual
x86_test-base
 
  Container 2
created #7005771
android_build
created #7005776
arm64_test
created #7005778
armhf_test
created #7005766
i386_build
created #7005759
kernel+rootfs_amd64
created #7005761
aarch64
kernel+rootfs_arm64
created #7005763
aarch64
kernel+rootfs_armhf
created #7005768
ppc64el_build
created #7005770
s390x_build
created #7005765
x86_build
created #7005773
x86_test-gl
created #7005775
x86_test-vk
 
  Meson X86 64
created #7005788
meson-clang
created #7005790
meson-clover
created #7005783
meson-clover-testing
created #7005785
meson-gallium
created #7005787
meson-release
created #7005780
meson-testing
created #7005781
meson-testing-asan
created #7005792
meson-vulkan
 
  Build Misc
created #7005793
meson-android
created #7005797
aarch64
meson-arm64
created #7005799
aarch64
meson-arm64-build-test
created #7005795
aarch64
meson-armhf
created #7005802
meson-i386
created #7005808
meson-mingw32-x86_64
created #7005806
kvm
meson-ppc64el
created #7005804
kvm
meson-s390x
created #7005801
allowed to fail
scons-win64
 
  Software Renderer
created #7005820
lavapipe-vk
created #7005818
llvmpipe-gles2
created #7005809
llvmpipe-piglit-cl
created #7005813
llvmpipe-piglit-glslparser
created #7005811
llvmpipe-piglit-quick_gl
created #7005814
llvmpipe-piglit-quick_shader
created #7005816
llvmpipe-traces
 
  Layered Backends
created #7005830
virgl-gl30-on-gl
created #7005832
virgl-gl31-on-gl
created #7005834
virgl-gl32-on-gl
created #7005823
virgl-gles2-on-gl
created #7005827
virgl-gles31-on-gl 1/2
created #7005828
virgl-gles31-on-gl 2/2
created #7005825
virgl-gles3-on-gl
created #7005821
virgl-traces