drm/xe/pat: annotate pat_index with coherency mode

Future uapi needs to give userspace the ability to select the pat_index
for a given vm_bind. However we need to be able to extract the coherency
mode from the provided pat_index to ensure it's compatible with the
cpu_caching mode set at object creation. There are various security
reasons for why this matters.  However the pat_index itself is very
platform specific, so seems reasonable to annotate each platform
definition of the pat table.  On some older platforms there is no
explicit coherency mode, so we just pick whatever makes sense.

v2:
  - Simplify with COH_AT_LEAST_1_WAY
  - Add some kernel-doc
v3 (Matt Roper):
  - Some small tweaks
v4:
  - Rebase
v5:
  - Rebase on Xe2 PAT additions
v6:
  - Rebase on removal of coh_mode from uapi

Bspec: 45101, 44235 #xe
Bspec: 70552, 71582, 59400 #xe2
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Pallavi Mishra <pallavi.mishra@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Filip Hazubski <filip.hazubski@intel.com>
Cc: Carl Zhang <carl.zhang@intel.com>
Cc: Effie Yu <effie.yu@intel.com>
Cc: Zhengguo Xu <zhengguo.xu@intel.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Pallavi Mishra <pallavi.mishra@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>