drm/xe/pat: Define PAT tables as static

The tables are only used within this file; there's no reason for them
not to be static.

Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://lore.kernel.org/r/20230327175824.2967914-1-matthew.d.roper@intel.com


Signed-off-by: Matt Roper <matthew.d.roper@intel.com>