drm/xe/pat: Move PAT setup to a dedicated file

drm/xe/pat: Move PAT setup to a dedicated file

PAT handling is growing in complexity and will continue to do so in
upcoming platforms.  Separate it out to a dedicated file to keep things
tidy.

The code is moved as-is here (aside from a few unused #define's that are
just dropped); further changes will come in future patches.

Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://lore.kernel.org/r/20230324210415.2434992-2-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>