[media] drxk: Make the QAM demodulator command parameters configurable

Currently there are two different implementations (in the firmware) for
the QAM demodulator command: one takes 4 and the other takes 2
parameters. The driver shows an error in dmesg When using the
4-parameter command with firmware that implements the 2-parameter
command. Unfortunately this happens every time when chaning the
frequency (on DVB-C).

This patch simply makes configurable, how many command parameters will
be used. All existing drxk_config instances using the "drxk_a3.mc" were
updated because this firmware is the only loadable firmware where the
QAM demodulator command takes 4 parameters. Some firmwares in the ROM
might also use it. The drxk instances in the em28xx-dvb driver were also
updated to silence the warnings.

If no qam_demod_parameter_count is given in the drxk_config struct, then
the correct number of parameters will be auto-detected.

[mchehab@redhat.com: Fix a small CodingStyle issue at one comment]
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Tested-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>