drm/xe/mtl: Handle PAT_INDEX offset jump

drm/xe/mtl: Handle PAT_INDEX offset jump

Starting with MTL, the number of entries in the PAT table increased to
16.  The register offset jumped between index 7 and index 8, so a slight
adjustment is needed to ensure the PAT_INDEX macros select the proper
offset for the upper half of the table.

Note that although there are 16 registers in the hardware, the driver is
currently only asked to program the first 5, and we leave the rest at
their hardware default values.  That means we don't actually touch the
upper half of the PAT table in the driver today and this patch won't
have any functional effect [yet].

Bspec: 44235
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://lore.kernel.org/r/20230324210415.2434992-7-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>