drm/xe/pat: Handle unicast vs MCR PAT registers

drm/xe/pat: Handle unicast vs MCR PAT registers

The PAT_INDEX registers are MCR registers on some platforms and unicast
on others.  On MTL the handling even varies between GTs:  the primary GT
uses MCR registers while the media GT uses unicast registers.  Let's add
proper MCR programming on the relevant platforms/GTs.

Given that we PAT tables to change pretty regularly on future platforms,
we'll make PAT programming an exception to the usual model of assuming
new platforms should inherit the previous platform's behavior.  Instead
we'll raise a warning if the current platform isn't handled in the
if/else ladder.  This should help prevent subtle cache misbehavior if we
forget to add the table for a new platform.

Bspec: 66534, 67609, 67788
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://lore.kernel.org/r/20230324210415.2434992-4-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>