virgl: Don't wait for read buffers if we can only wait for writes

If we only read a buffer, we don't need to wait for pending reads to this
buffer, only pending writes. This can reduce the wait time in some cases.

For the gun3D trace, this speeds up the trace from ~100 fps to ~142fps.

Signed-off-by: Stéphane Marchesin <marcheu@chromium.org>
43 jobs for !8483 with gun3d_0001 in 14 seconds (queued for 2 seconds)
latest detached
Status Name Job ID Coverage
  Sanity
failed sanity #6638771

00:00:14

 
  Container
skipped arm_build #6638774
aarch64 manual
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manual
skipped windows_build_vs2019 #6638776
windows shell 1809 mesa manual
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manual
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manual
 
  Container 2
skipped android_build #6638784
skipped arm64_test #6638787
skipped armhf_test #6638788
skipped i386_build #6638781
skipped kernel+rootfs_amd64 #6638777
skipped kernel+rootfs_arm64 #6638778
aarch64
skipped kernel+rootfs_armhf #6638779
aarch64
skipped ppc64el_build #6638782
skipped s390x_build #6638783
skipped x86_build #6638780
skipped x86_test-gl #6638785
skipped x86_test-vk #6638786
 
  Meson X86 64
skipped meson-clang #6638794
skipped meson-clover #6638795
skipped meson-clover-testing #6638791
skipped meson-gallium #6638792
skipped meson-release #6638793
skipped meson-testing #6638789
skipped meson-testing-asan #6638790
skipped meson-vulkan #6638796
 
  Build Misc
skipped meson-android #6638797
skipped meson-arm64 #6638799
aarch64
skipped meson-arm64-build-test #6638800
aarch64
skipped meson-armhf #6638798
aarch64
skipped meson-i386 #6638802
skipped meson-mingw32-x86_64 #6638805
skipped meson-ppc64el #6638804
kvm
skipped meson-s390x #6638803
kvm
skipped scons-win64 #6638801
allowed to fail
 
  Layered Backends
skipped virgl-gl30-on-gl #6638811
skipped virgl-gl31-on-gl #6638812
skipped virgl-gl32-on-gl #6638813
skipped virgl-gles2-on-gl #6638807
skipped virgl-gles31-on-gl 1/2 #6638809
skipped virgl-gles31-on-gl 2/2 #6638810
skipped virgl-gles3-on-gl #6638808
skipped virgl-traces #6638806
 
Name Stage Failure
failed
sanity Sanity
No job log