gbm: Add support for 10bpp BGR formats

Add support for XBGR2101010 and ABGR2101010 formats.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Tested-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Tested-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>