media: rockchip: rga: rework buffer handling for multi-planar formats

Multi-planar formats may have multiple planes that must be handled and
correctly mapped into a continuous buffer for the RGA by using the DMA
descriptors.

The plane offsets in the continuous mapping may now start at page
boundaries and the previous calculation based on the frame sizes is only
valid for planar buffers in a single memory. Therefore, the offsets must
be detected and set while creating the mapping.

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