[media] m5mols: Implement .get_frame_desc subdev callback

.get_frame_desc can be used by host interface driver to query
properties of captured frames, e.g. required memory buffer size.

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>