Prevents large clock on AOD from overflowing top of screen.

This works on AOD since notification icons were moved to
the status bar. For the lock screen, the clock is made
transparent due to the height of the clock. This prevents
the clock from interfering with the notifs in stack scroller.

Bug: b119103421
Test: KeyguardClockPositionAlgorithmTest updated.
Change-Id: Ife2de31ae6d55effced99c6d419c794ac57c8522