Don't show home controls complication if not available.

There is a toggle to disable home controls in Settings, and we need to
honor that toggle when determining if the complication should be shown
on the dream.

Bug: 278964460
Test: atest DreamOverlayStateControllerTest
Test: flashed device and disabled toggle in settings, verified home
controls does not show on clock dream

Change-Id: I4e72f4619fd0ebbf5a78620796f0114ceabc9365