[media] soc_camera/mx3_camera.c: move to staging in preparation, for removal

This driver is deprecated: it should become a stand-alone driver
instead of using the soc-camera framework.

Unless someone is willing to take this on (unlikely with such
ancient hardware) it is going to be removed from the kernel
soon.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>