Support keyguard slice views

The views themselves, while added, were not fully initialized,
leaving the content empty. Also make sure burn in movements apply
and that it updates with each time tick.

Fixes: 439890240
Test: AOSP build to show media + date
Flag: EXEMPT bugfix
Change-Id: Ic9b4686a3d51efe18ba0063a9a66131f4fe77abf