iris: Avoid extra CCS_E flushes for aux mode changes

iris: Avoid extra CCS_E flushes for aux mode changes

We're going to start toggling between FCV_CCS_E and CCS_E. When
switching aux modes, flush_previous_aux_mode would typically perform
cache flushes for good reason. In the case of switching between CCS_E
with FCV on vs off, we haven't found aux mode flushing to matter. Treat
both CCS_E variants as equivalent to avoid extra cache flushing.

Reviewed-by: Rohan Garg <rohan.garg@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23220>