[media] s5p-fimc: Add device tree support for the media device driver

This patch adds changes required for the main camera media device
driver corresponding to the top level 'camera' device node.
The drivers of devices corresponding to child nodes of the 'camera'
node are looked up and and registered as sub-devices to the top
level driver. The main driver's probing is deferred if any of the
sub-device drivers is not yet initialized and ready.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>