Prevent adding duplicate callbacks to the state controller

- KeyguardBottomAreaView can add itself multiple times as a callback,
  which can leak a bitmap via that view if the state controller keeps
  an extra ref to it.

Bug: 141555865
Bug: 140629244
Test: Change overlays multiple times, take heap dump and ensure no
      leaked bitmaps

Change-Id: I8169eac24d8801ae71e4bdc60a16c68eb3896cc4