drm/xe: Return GMD_ID revid properly

drm/xe: Return GMD_ID revid properly

peek_gmdid() returns the IP version, not the raw value of the GMD_ID
register.  Make sure we extract and return the rev_id field as well so
that it can be used to determine the IP steppings properly.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://lore.kernel.org/r/20230614205202.3376752-2-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>