[media] v4l: vsp1: Add alpha channel support to the memory ports

Support ARGB formats on the RPF side by reading the alpha component from
memory and on the WPF side by writing it to memory.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>