drm/xe: Optimize flushing of L2$ by skipping unnecessary page reclaim

drm/xe: Optimize flushing of L2$ by skipping unnecessary page reclaim

There are additional hardware managed L2$ flushing such as the
transient display. In those scenarios, page reclamation is
unnecessary resulting in redundant cacheline flushes, so skip
over those corresponding ranges.

v2:
 - Elaborated on reasoning for page reclamation skip based on
   Tejas's discussion. (Matthew A, Tejas)

v3:
 - Removed MEDIA_IS_ON due to racy condition resulting in removal of
   relevant registers and values. (Matthew A)
 - Moved l3 policy access to xe_pat. (Matthew A)

v4:
 - Updated comments based on previous change. (Tejas)
 - Move back PAT index macros to xe_pat.c.

Signed-off-by: Brian Nguyen <brian3.nguyen@intel.com>
Reviewed-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20251212213225.3564537-21-brian3.nguyen@intel.com