libcamera: v4l2_videodevice: Coalesce planes when queuing buffer

When queueing a buffer to a V4L2VideoDevice, the number of planes in the
FrameBuffer may not match the number of V4L2 buffer planes if the
PixelFormat is multi-planar (has multiple colour planes) and the V4L2
format is single-planar (has a single buffer plane). In this case, we
need to coalesce all FrameBuffer planes into a single V4L2 buffer plane.
Do so, and add validity checks to reject frame buffers that can't be
described using a single V4L2 buffer plane.

This change prepares for proper multi-planar support, but isn't expected
to result in a change of behaviour with existing pipeline handlers, as
none of them queue an output buffer with multiple FrameBuffer planes or
use non-contiguous buffers for either capture or output.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>

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