[media] soc_camera: add control handler support

The soc_camera framework is switched over to use the control framework.
After this patch none of the controls in subdevs or host drivers are available,
until those drivers are also converted to the control framework.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
[g.liakhovetski@gmx.de: moved code around, fixed problems]
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>