[media] s5p-fimc: Don't allocate fimc-m2m video device dynamically

There is no need to to dynamically allocate struct video_device
for the M2M devices, so embed it instead in driver's private
data structure as it is done in case of fimc-capture and fimc-lite,
where it solves some bugs on cleanup paths.

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>