media: soc_camera: Move to the staging tree

The SoC camera framework has no functional drivers left, something that
has not changed for years. Move the leftovers to the staging tree.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>