Bluetooth: Add support for controller specific logging

To enable controller specific logging, the userspace daemon has to have
the ability to log per controller. To facilitate this support, provide
a dedicated logging channel. Messages in this channel will be included
in the monitor queue and with that also forwarded to monitoring tools
along with the actual hardware traces.

All messages from the logging channel are timestamped and with that
allow an easy correlation between userspace messages and hardware
events. This will increase the ability to debug problems faster.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>