make recovery reboot after 2 minutes of no activity

If recovery sits for 2 minutes in prompt_and_wait(), and you've never
turned the screen on via the magic keypress, go ahead and reboot.  (We
used to assume that the user could pull the battery to get out of this
state, but on devices with nonremovable batteries...)

If you've ever enabled display of the log/menu since recovery started,
we assume you know what you're doing and will stay in recovery until
you choose to reboot.

Bug: 3387873
Bug: 3387274
Change-Id: I041621e5db132df9a925e6808845a7c45e1b427a