drm/xe: directly use pat_index for pte_encode

In a future patch userspace will be able to directly set the pat_index
as part of vm_bind. To support this we need to get away from using
xe_cache_level in the low level routines and rather just use the
pat_index directly.

v2: Rebase
v3: Some missed conversions, also prefer tile_to_xe() (Niranjana)
v4: remove leftover const (Lucas)

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Cc: Pallavi Mishra <pallavi.mishra@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Pallavi Mishra <pallavi.mishra@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>