There are some ifdefs inside the dvb_demux that are meant to
enable advanced debug capabilities, at the cost of being very
verbose.

Keeping those as internal ifdefs is a very bad idea, as it
doesn't make easy to check if the code there was broken by
some patch. So, let's add an explicit Kconfig option for it.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>