v4l: vsp1: Switch to XRGB formats

v4l: vsp1: Switch to XRGB formats

The driver ignores the alpha component on output video nodes and
hardcodes the alpha component to 0 on capture video nodes. Make this
explicit by exposing XRGB formats.

Compatibility with existing userspace applications is handled by
selecting the XRGB format corresponding to the requested old RGB format.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
(cherry picked from commit 56bfef3e72cf4a98d0e8f56129673146733c1366)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>