x86/gpu: add RKL stolen memory support

RKL re-uses the same stolen memory registers as TGL and ICL.

Bspec: 52055
Bspec: 49589
Bspec: 49636
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200504225227.464666-3-matthew.d.roper@intel.com