[media] adv7180: add more subdev video ops

Add subdev video ops for ADV7180 video decoder.  This makes decoder usable on
the soc-camera drivers.
[Sergei: renamed adv7180_try_mbus_fmt() to adv7180_mbus_fmt().]

Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>