Always bind slice on background

Doing on the main thread will increase jank
when unlocking or waking up.

Fixes: 71543966
Test: runtest systemui-jank -c android.platform.systemui.tests.jank.SystemUiJankTests -m testAmbientWakeUp
Change-Id: I3b534425c85609a132d33905de18dbc36fd37f0d