Also go to sleep when dozing

Since always-on-screen shows over an occluded activity, we also
need to go to sleep to in that case. Now, we could introduce
another sleep token that's controlled by SystemUI. But that's a
bit complicated. It's much simpler to unconditionally go to sleep
whenever we are dozing.

Test: With always-on-device, open occluded activity, turn off
screen, make sure activity pauses.
Fixes: 62679291

Change-Id: Icd64037d33cc523e498a0a9f5f7df939304e02ed