V4L/DVB (12506): soc-camera: convert to platform device

Convert soc-camera core and all drivers to platform device API. We already
converted platforms to register a platform device for each soc-camera client,
now we remove the compatibility code and switch completely to the new scheme.
This is a preparatory step for the v4l2-subdev conversion.

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