V4L/DVB: V4L2: sh_mobile_camera_ceu: add support for CSI2

Using CEU with CSI2 on SH-Mobile requires some special configuration of the
former. We also have to switch from calling only one subdev .s_mbus_fmt and
.try_mbus_fmt to calling all subdevices. Take care to increment CSI2 driver
use count to prevent it from unloading, while in use.

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