privatize keyguard transparency observer

-Vanir

Change-Id: I61e0e695fd56d8fc29169b4a714867c6f166b4c2
remove some read/write time for hardware key devices on initialization

this commit moves updateSettings(); out of the observer and to the end of
the try/finally block where it's called to be observed since devices with
hardware keys prior to this commit would have been doing twice the read/writes
to observe the registered settings

Change-Id: I8cfad7395663fc08b4ee7311d7671ee6e76e3dcf