Keep scrim black when "always on" is off

The first frame when waking up is expensive and we
need a black scrim hiding what was left behind.

Bug: 78022321
Test: atest packages/SystemUI/tests/src/com/android/systemui/statusbar/phone/ScrimControllerTest.java
Change-Id: I99e2b7960daf2cbe51bec6aee4b15c74d532078c