[media] v4l: Add ARGB and XRGB pixel formats

The existing RGB pixel formats are ill-defined in respect to their alpha
bits and their meaning is driver dependent. Create new standard ARGB and
XRGB variants with clearly defined meanings and make the existing
variants deprecated.

The new pixel formats 4CC values have been selected to match the DRM
4CCs for the same in-memory formats.

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