drm/xe: Fake pulling gt->info.engine_mask from hwconfig blob

The blob doesn't fully support this yet, so fake for now to ensure our
driver load order is correct.

Once the blob supports pulling gt->info.engine_mask from the blob, this
patch can be removed.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>