dvb: mpq: Secure demux log level

Add secure demux API allowing to set log level verbosity.
Log level can be set from user-sapce via a debugfs entry.
Default is no logging.

Change-Id: I80f3900f1788f54f02904fc7a4b317cc7c06a6db
Signed-off-by: Gilad Broner <gbroner@codeaurora.org>