media: imx-jpeg: Support contiguous and non contiguous format

mxc-jpeg supports non contiguous format nv12m,
and in order to compatible with the devices
that only support contiguous format nv12,
jpeg can support nv12 and nv12m in the same time.

Signed-off-by: Ming Qian <ming.qian@nxp.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil: document is_rgb variable]