Vext1_On

The external Vext1 power is on.  Many boards have auxillary power rails that the CPU turns on only
occasionally.  In cases where that rail has multiple devices on it we usually want to have logging on
the state of that rail as an independent record.
For instance on the Heltec Tracker 1.1 board, this rail is the power source for the GPS and screen.

The log messages will be short and complete (see PowerMon.Event in the protobufs for details).
something like "S:PM:C,0x00001234,REASON" where the hex number is the bitmask of all current states.
(We use a bitmask for states so that if a log message gets lost it won't be fatal)