[media] dt3155v4l: move vb2_queue to top-level

Instead of initializing the vb2_queue in open (and freeing in release)
do this in probe/remove instead. And as a bonus use the vb2 helper
functions to greatly simplify the driver.

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