drm/xe/pat: Keep track of relevant indexes

Some of the PAT entries are relevant for internal driver use, which
varies per platform. Let the PAT early initialization set what they
should point to so the rest of the driver can use them where needed.

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20230927193902.2849159-9-lucas.demarchi@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>