drm/xe: Reinstate media GT support

Now that tiles and GTs are handled separately and other prerequisite
changes are in place, we're ready to re-enable the media GT.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20230601215244.678611-31-matthew.d.roper@intel.com


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