drm/xe: Use pat_index to encode pde/pte

Change the xelp_pte_encode() and xelp_pde_encode() functions to use the
platform-dependent pat_index.  The same function can be used for all
platforms as they only need to encode the pat_index bits in the same
pte/pde layout. For platforms that don't have the most significant bit,
as long as they don't return a bogus index they should be fine.

v2: Use the same logic to encode pde as it's compatible with previous
    logic, it's more future proof and also fixes the cache setting for
    PVC (Matt Roper)

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20230927193902.2849159-10-lucas.demarchi@intel.com


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