dvb: add a tristate to allow set higher/normal LNBf voltage

Some DVB devices have an optional ioctl that allows changing
between normal voltage for LNBf (13V/18V) to a higher voltage
mode (usually, 14V/19V), meant to compensate for voltage loss
on long cabling. Without that, it is not possible to properly
switch the polarization.

Add a tristate check box to allow enabling/disabling this via
ioctl.

BUG: 374693

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>