media: rzg2l-cru: video: Implement .link_validate() callback

Implement the `.link_validate()` callback for the video node and move the
format checking into this function. This change allows the removal of
`rzg2l_cru_mc_validate_format()`.

Note, the fmt.format.code and fmt.format.field checks have be dropped as
the subdev .set_fmt() handler ensures that those fields always hold valid
values.

Suggested-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20241018133446.223516-19-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>