[media] dvb-frontends/cxd2841er: optionally tune earlier in set_frontend()

When AUTO_IFHZ is set and the tuner is supposed to provide proper IF speed
values, it should be possible to have the tuner setup take place before
the demod is configured, else the demod might be configured with either
wrong (old), or even no values at all, which obviously will cause issues.
To set this behaviour in the most flexible way, this is done with a
separate flag instead of making this depend on AUTO_IFHZ.

It should be evaluated if tuning shouldn't take place earlier in all cases
and hardware constellations.

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>