[media] saa7134-go7007: convert to a subdev and the control framework

The only thing missing after this to make the Sensoray model 614 board work is
to hook it up to the saa7134 driver, but that will have to wait until this
driver goes out of staging.

Signed-off-by: Pete Eberlein <pete@sensoray.com>
[hans.verkuil@cisco.com: updated to make it merge correctly]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>