[media] soc-camera: split struct soc_camera_link into host and subdevice parts

struct soc_camera_link currently contains fields, used both by sensor and
bridge drivers. To make subdevice driver re-use simpler, split it into a
host and a subdevice parts.

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