V4L/DVB (12519): soc-camera: put pixel format initialisation back in probe, add .put_formats()

The move of format translation initialisation into soc_camera_open() was
temporary for the soc-camera as platform driver intermediate step, put it back
into soc_camera_probe(). Also add a .put_formats() method to
soc_camera_host_ops to free any resources host driver might have allocated in
.get_formats().

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>