Add LVDS RGB media bus formats

This patch adds three new RGB media bus formats that describe
18-bit or 24-bit samples transferred over an LVDS bus with three
or four differential data pairs, serialized into 7 time slots,
using standard SPWG/PSWG/VESA or JEIDA data ordering.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>