For case-closed debug, the 'power_state:rec' servo control can be
problematic for some hardware designs, in that the device can only
boot from USB by disabling charging and running on battery.  In order
for such hardware to be testable in the lab, we have to make sure
that there's a way to get back onto AC power.

The specification for any new behaviors will be worked out in bug
753074.  Once the details there are worked out, we need to implement
servod changes to match the specification.

(Assigning initially to Firmware>EC, because it seems there's no
component for the PD).