dri: Use DRM_FORMAT_* instead of defining our own copy.

dri: Use DRM_FORMAT_* instead of defining our own copy.

We have only two defines that aren't from DRM_FORMAT_*: SARGB and
SABGR.  Keep only those as __DRI_IMAGE_FOURCC and garbage collect the
rest.

While this header is also used from the X server, the X server doesn't
use any __DRI_IMAGE enums.

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>