Task Manager shutdown
---------------------

In order to make shutdown more reliable and allow applications to force a
reboot, the Task Manager shutdown controls have been updated. In addition
to the standard bits that may be passed to TaskManager_Shutdown, new bits
have been defined to provide additional functions.

TaskManager_Shutdown
=> R0 = flags :
           0   Do not display restart dialogue
           1   Do not broadcast Message_PreQuit to clients
           2   Flag in CMOS as a power down due to exceptional condition
               (eg lack of power)
           3   Send Message_Shutdown to all tasks
           4   Reject media requests (OS_UpCall 1 and 2)
           5   After shutdown has completed, reboot machine
           6   After shutdown has completed, power off machine
         other Reserved

This SWI is used to request that the machine shutdown.
Note: The power off facilities are not present on existing hardware and
      as such will not function.
