[media] s5p-mfc: v4l2 controls setup routine moved to initialization code

Callback .start_streaming is called once for every queue,
so v4l2_ctrl_handler_setup was called twice during stream start.
Moving v4l2_ctrl_handler_setup to context initialization
reduces numbers of calls and seems to be more consistent with API.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>