[media] cx25821: setup output nodes correctly

Drop the custom ioctls and enable the video output nodes again, this time
using standard ioctls.
The next step will be to provide a proper write() interface.

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