[media] dvb-frontends/cxd2841er: replace IFFREQ calc macros into functions

The way the MAKE_IFFREQ_CONFIG macros are written make it impossible to
pass regular integers for iffreq calculation, since this will cause "SSE
register return with SSE disabled" compile errors. This changes the
calculation into C functions which also might help when debugging. Also,
expand all passed frequencies from MHz to Hz scale.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Acked-by: Abylay Ospan <aospan@netup.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>