[media] V4L: soc-camera: make (almost) all client drivers re-usable outside of the framework

The most important change in this patch is direct linking to struct
soc_camera_link via the client->dev.platform_data pointer. This makes most
of the soc-camera client drivers also usable outside of the soc-camera
framework. After this change all what is needed for these drivers to
function are inclusions of soc-camera headers for some convenience macros,
suitably configured platform data, which is anyway always required, and
loaded soc-camera core module for library functions. If desired, these
library functions can be made generic in the future and moved to a more
neutral location.

The only two client drivers, that still depend on soc-camera are:

mt9t031: it uses struct video_device for its PM. Since no hardware is
available, alternative methods cannot be tested.

ov6650: it uses struct soc_camera_device to pass its sense data back to
the bridge driver. A generic v4l2-subdevice approach should be developed
to perform this.

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