One line per format, and using the same layout.

This also removes the special case for RGB565, only ARGB8888 and
XRGB8888 need to be special-cased.

Signed-off-by: Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
Reviewed-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Olivier Fourdan <ofourdan@redhat.com>