[media] s5p-fimc: Add subdev for the FIMC processing block

Add a subdev to expose the host's scaling and composition functions.
The camera frame composition onto an output buffer may be configured
through set/get_crop at FIMC.{n} source pad.
Additionally allow crop, composition and controls to be modified
during streaming. Make sure the default format is set when opening
the video capture node.
Rename struct fimc_vid_cap::fmt to more relevant 'mf' to avoid
confusion.

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