media: dvb: represent min/max/step/tolerance freqs in Hz

Right now, satellite frontend drivers specify frequencies in kHz,
while terrestrial/cable ones specify in Hz. That's confusing
for developers.

However, the main problem is that universal frontends capable
of handling both satellite and non-satelite delivery systems
are appearing. We end by needing to hack the drivers in
order to support such hybrid frontends.

So, convert everything to specify frontend frequencies in Hz.

Tested-by: Katsuhiro Suzuki <suzuki.katsuhiro@socionext.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>