[media] soc-camera: switch to using the new struct v4l2_subdev_platform_data

This prepares soc-camera to use struct v4l2_subdev_platform_data for its
subdevice-facing API, which would allow subdevice driver re-use.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>