[media] e4000: implement V4L2 subdevice tuner and core ops

Implement V4L2 subdevice tuner and core ops. After that this driver
is hybrid driver implementing both V4L2 and DVB ops.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>