V4L/DVB: em28xx: add Dikom DK300 hybrid USB tuner

Adds digital and analogue tv support for Dikom DK300 hybrid usb card.

Not working: remote controller

To be done: it seems that with the proposed patch the digital demodulator
remains activated if the tuner is switched from digital to analogue mode.

Workaround is to unplug and replug the device when switching from digital to
analogue. If someone can explain how to verify the gpio settings using the
usbsnoop, the above issue perhaps can be resolved.

Signed-off-by: Andrea Amorosi <Andrea.Amorosi76@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>