When there is a positive or negative transition of Vbus, we Shall reduce
our power consumption to no more than 2.5 W beforehand. This can be
easily achieved in all cases by simply turning off the output. This was
implemented, so that's one fewer Shall we aren't doing.
In the process, I made some API changes for the Device Policy Manager.
No more output_on() and output_off(), now it's output_set(true) and
output_set(false), plus a special case output_default() used during a
hard reset. This much better matches how these functions are used by
the policy engine.