V4L/DVB (4606): Add driver for TUA6100

This driver was originally in budget-av.c, however I have extracted it into
a seperate file to permit reuse.
I also reworked the code to make it maintainable. I then examined the KNC1
windows drivers and rewrote the code in order to configure the PLL as they
do. This solves a lot of reported tuning problems.

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