[media] v4l: add type field to v4l2_modulator struct

Add type field to that struct like it counterpart v4l2_tuner
already has. We need type field to distinguish different tuner
types from each others for transmitter too.

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