media: rockchip: rga: switch to multi-planar API

Switch to the multi-planar API, which allows to handle buffers with
separate planes.

The RGA driver doesn't expose multi-planar formats, yet. The existing
contiguous planar formats can be used with the multi-planar API as well,
but the multi-planar API is required for multi-planar formats.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>