drm/xe/pat: Consolidate PAT programming logic for pre-Xe2 and post-Xe2

Now that the PAT settings for the new special entries introduced by Xe2
are decided during early software init and left NULL on platforms they
don't apply to, there's no need to keep separate programming functions
for pre-Xe2 and post-Xe2 platforms.  Consolidate down to a single pair
of programming functions (mcr and non-mcr) that can be used on any
platform.

Reviewed-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Link: https://lore.kernel.org/r/20250613214751.792066-4-matthew.d.roper@intel.com


Signed-off-by: Matt Roper <matthew.d.roper@intel.com>