iris: Avoid sampling some MCS surfaces with clear

Supposedly avoids GPU hangs in BF4. See HSD 1707282275 and 14013111325.

v2. Fix bug in WA implementation. (Sagar)

Cc: mesa-stable
35 jobs for !8755 with fix/tgl-mcs-fc-sample in 14 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Sanity
passed #7075125
sanity

00:00:14

 
  Container
manual #7075128
aarch64 manual
arm_build
manual #7075129
manual
arm_test-base
manual #7075130
windows shell 1809 mesa manual
windows_build_vs2019
manual #7075126
manual
x86_build-base
manual #7075127
manual
x86_test-base
 
  Container 2
created #7075138
android_build
created #7075141
arm64_test
created #7075142
armhf_test
created #7075135
i386_build
created #7075131
kernel+rootfs_amd64
created #7075132
aarch64
kernel+rootfs_arm64
created #7075133
aarch64
kernel+rootfs_armhf
created #7075136
ppc64el_build
created #7075137
s390x_build
created #7075134
x86_build
created #7075139
x86_test-gl
created #7075140
x86_test-vk
 
  Meson X86 64
created #7075148
meson-clang
created #7075149
meson-clover
created #7075145
meson-clover-testing
created #7075146
meson-gallium
created #7075147
meson-release
created #7075143
meson-testing
created #7075144
meson-testing-asan
created #7075150
meson-vulkan
 
  Build Misc
created #7075151
meson-android
created #7075153
aarch64
meson-arm64
created #7075154
aarch64
meson-arm64-build-test
created #7075152
aarch64
meson-armhf
created #7075156
meson-i386
created #7075159
meson-mingw32-x86_64
created #7075158
kvm
meson-ppc64el
created #7075157
kvm
meson-s390x
created #7075155
allowed to fail
scons-win64