V4L/DVB (5361): Dvb-pll: Fix Kconfig files and allow dvb-pll to be optional

V4L/DVB (5361): Dvb-pll: Fix Kconfig files and allow dvb-pll to be optional

A number of drivers selected DVB_PLL when they did not need it, and some
that did need it did not select it.

The DVB_PLL option is given a name and help text, so that it will show up
in the config menu.  DVB_PLL support can be turned on if an out-of-tree
driver needs it.

The standard dvb fe customization support is added to dvb-pll.h.  Since
all modules which select DVB_PLL do so unconditionally, it is not
possible to turn dvb-pll off when an enabled module selects it, unlike
most of the other frontend/tuner drivers.  This is because the users of
dvb-pll have static references to dvb-pll symbols other than the attach
function.  If these references are removed, then dvb-pll will be
disablable as the other frontend/tuner drivers are.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>