iris: Enable fragment shader interlock on Gen9+.

There's some debate about whether we should support this on older
hardware as well.  Currently i965 turns it off on Gen8- though, so
we follow suit.  If this changes, we can update this as well.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
10 jobs for !864 with iris-interlock in 9 minutes and 55 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Containers Build
passed #299240
debian

00:00:24

 
  Build+Test
passed #299242
meson-clang

00:09:30

passed #299246
meson-clover

00:08:13

passed #299245
meson-main

00:07:03

passed #299241
meson-swr-glvnd

00:05:34

passed #299247
meson-vulkan

00:02:54

passed #299249
scons-llvm

00:05:29

passed #299248
scons-nollvm

00:03:16

passed #299243
scons-swr

00:05:35

passed #299244
scons-win64

00:09:04