drm/xe/mtl: Map PPGTT as CPU:WC

drm/xe/mtl: Map PPGTT as CPU:WC

On MTL and beyond, the GPU performs non-coherent accesses to the PPGTT
page tables.  These page tables should be mapped as CPU:WC.

Removes CAT errors triggered by xe_exec_basic@once-basic on MTL:

   xe 0000:00:02.0: [drm:__xe_pt_bind_vma [xe]] Preparing bind, with range [1a0000...1a0fff) engine 0000000000000000.
   xe 0000:00:02.0: [drm:xe_vm_dbg_print_entries [xe]] 1 entries to update
   xe 0000:00:02.0: [drm:xe_vm_dbg_print_entries [xe]]  0: Update level 3 at (0 + 1) [0...8000000000) f:0
   xe 0000:00:02.0: [drm] Engine memory cat error: guc_id=2
   xe 0000:00:02.0: [drm] Engine memory cat error: guc_id=2
   xe 0000:00:02.0: [drm] Timedout job: seqno=4294967169, guc_id=2, flags=0x4

v2:
 - Rename to XE_BO_PAGETABLE to make it more clear that this BO is the
   pagetable itself, rather than just being bound in the PPGTT.  (Lucas)

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://lore.kernel.org/r/20230725003433.1992137-3-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>