Add format definition and required plumbing to create images.
Note that there is no match to drm_fourcc definition, just like
with existing _DRI_IMAGE_FOURCC_SARGB8888.
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>