Extend the AR71XX watchdog debugging and data.
Extend the AR71XX watchdog debugging and data.

* Add some per-device sysctl entries which record the watchdog state -
  whether it is armed; whether the last reboot was due to the watchdog.
* Add a per-device sysctl debug flag to enable logging watchdog arming/
  disarming.

Reviewed by:	gonzo@

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase