[media] v4l: vsp1: Factorize media bus codes enumeration code

Most of the entities can't perform format conversion and implement the
same media bus enumeration function. Factorize the code into a single
implementation.

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