don't call hwc with non-empty layer lists for blanked displays

we now make sure to take the blanked state of a display into
account when we build its list of visible layers, this ensures
that we won't call prepare/set with a non-empty list when the
display is blanked.

Possibly fixes 7075380, 7103553, 7130187, 7016215

Bug: 7075380
Change-Id: I9fdd2e73d1b7621eaeca3d4ac2ae60d9fb1b3631