iris: Use ISL_AUX_USAGE_GEN12_CCS_E on gen12

Makes iris pass a subtest of the fcc-write-after-clear piglit test
(fast-clear tracking across layers 1 -> 0 -> 1) on gen12.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5363>
3 files changed