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 <firstname.lastname@example.org> Reviewed-by: Kristian H. Kristensen <email@example.com>