intel: Relax scheduling dependencies for ARF access.

We were treating them as scheduling barriers, but since they weren't
included in is_scheduling_barrier(), it meant that each access would add
deps from the beginning to the end of the block, for some awful O(n^2)
performance.

Reduces runtime of
dEQP-VK.binding_model.buffer_device_address.set3.depth3.basessbo.convertchecku64.nostore.single.std140.frag
from 9.9s to 2.0s on my SKL system, and should let us take the test group
off the skip list in Chrome OS due to timeouts.

shader-db:
total instructions in shared programs: 9043717 -> 9043725 (<.01%)
instructions in affected programs: 948 -> 956 (0.84%)
total cycles in shared programs: 403834893 -> 403766806 (-0.02%)
cycles in affected programs: 103629173 -> 103561086 (-0.07%)
total spills in shared programs: 4036 -> 4037 (0.02%)
spills in affected programs: 28 -> 29 (3.57%)
total fills in shared programs: 3221 -> 3224 (0.09%)
fills in affected programs: 89 -> 92 (3.37%)

Closes: #4648
33 jobs for !10396 with intel-arf-deps in 11 seconds (queued for 3 seconds)
latest detached
Status Job ID Name Coverage
  Sanity
passed #9098676
sanity

00:00:11

 
  Container
manual #9098679
aarch64 manual
arm_build
manual #9098680
windows shell 1809 mesa manual
windows_build_vs2019
manual #9098677
manual
x86_build-base
manual #9098678
manual
x86_test-base
 
  Container 2
created #9098685
android_build
created #9098682
i386_build
created #9098688
kernel+rootfs_amd64
created #9098689
aarch64
kernel+rootfs_arm64
created #9098690
aarch64
kernel+rootfs_armhf
created #9098683
ppc64el_build
created #9098684
s390x_build
created #9098681
x86_build
created #9098686
x86_test-gl
created #9098687
x86_test-vk
 
  Meson X86 64
created #9098696
meson-clang
created #9098697
meson-clover
created #9098693
meson-clover-testing
created #9098694
meson-gallium
created #9098695
meson-release
created #9098691
meson-testing
created #9098692
meson-testing-asan
created #9098698
meson-vulkan
 
  Build Misc
created #9098699
arm_test
created #9098700
meson-android
created #9098702
aarch64
meson-arm64
created #9098703
aarch64
meson-arm64-asan
created #9098704
aarch64
meson-arm64-build-test
created #9098701
aarch64
meson-armhf
created #9098705
meson-i386
created #9098708
meson-mingw32-x86_64
created #9098707
meson-ppc64el
created #9098706
kvm
meson-s390x