dri: add __DRI_IMAGE_FORMAT_SXRGB8

Add format definition and required plumbing to create images.

Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3077>
3 files changed