V4L/DVB (13458): go7007: subdev conversion

Convert the go7007 driver to v4l2 subdev interface, using v4l2 i2c
subdev functions instead of i2c functions directly.  The v4l2 ioctl ops
functions call subdev ops instead of i2c commands.

Signed-off-by: Pete Eberlein <pete@sensoray.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>