[media] vivid: the overlay API wasn't disabled completely for multiplanar

If the vivid driver is loaded in multiplanar mode, then the capture overlay
functionality should be disabled. This wasn't fully done, which led to
v4l2-compliance errors.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>