drm/xe: Track whether platform has LLC

Some driver initialization is conditional on the presence of an LLC.
Add an extra feature flag to support this.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20230410183910.2696628-2-matthew.d.roper@intel.com


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