[media] v4l: Add RBG and RGB 8:8:8 media bus formats on 24 and 32 bit busses

Add support and documentation for two media bus formats:
MEDIA_BUS_FMT_RBG888_1X24 and MEDIA_BUS_FMT_RGB888_1X32_PADHI

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>