media: rkvdec: Add image format concept

Add an enum rkvdec_image_fmt used to signal an image format, e.g.
4:2:0 8-bit, 4:2:0 10-bit or any.

Tag each supported CAPUTRE format with an image format and use this tag
to filter out unsupported CAPTURE formats.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Tested-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Tested-by: Christopher Obbard <chris.obbard@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>