Make sure onScreenTurnedOn is called at power on.

KeyguardViewMediator.onScreenTurnedOn is not called if the device is
booted into the power-on state. In this case mScreenOn remains false
and the lockscreen will always appear after outgoing calls. This fix
ensures that onScreenTurnedOn is called when the device is powered
up in the on state.

Fixes bug 6709173.

Change-Id: I7557d8f002307b9125bc53b13bc3cb4c5c9b2758