V4L/DVB (3881): Convert core dvb-usb pll code to refactored tuner code

Rename pll calls to appropriate tuner calls.
Add pll gate control calls where appropriate.

Signed-off-by: Andrew de Quincey <adq_dvb@lidskialf.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>