drm/xe: highlight reserved PAT entries in dump output

drm/xe: highlight reserved PAT entries in dump output

Enhance the PAT table dump by marking reserved entries with an
asterisk (*) for improved readability and debugging.

V2:
  Added a note in the "PAT table" header explaining the meaning of
the asterisk(*) to improve clarity for readers. (Matt Roper)

V3:
  Introduced a valid field in struct xe_pat_table_entry to
explicitly track whether an entry is valid or reserved, avoiding
reliance on coh_mode == 0. (Matt Roper)

Signed-off-by: Xin Wang <x.wang@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patch.msgid.link/20251030221734.1058350-1-x.wang@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>