drm/xe: Use vfunc for ggtt pte encoding

Use 2 different functions for encoding the ggtt's pte, assigning them
during initialization. Main difference is that before Xe-LPG, the pte
didn't have the cache bits.

v2: Re-use xelp_ggtt_pte_encode_bo() for the common part with
    xelpg_ggtt_pte_encode_bo() (Matt Roper)

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20230927193902.2849159-11-lucas.demarchi@intel.com


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