Reported by Joerg Reisenweber, Sep 1, 2014

Shutting down modem power by an external switch can create issues 
with both modem's internal flash as well as the flash in SIM.

To mitigate, we should give modem a chance to shut down gracefully 
before we cut power.

To implement, I suggest:
1) asserting EMERGENCY_SHUTDOWN as soon as SoC shuts down the 
external power switch by toggling the control line.
2) delay on->off transition of actual power switch by a maybe 1s 
after SoC toggled the control line