Controls: Add a temporary space for home controls integration

This space will only be visible by setting a flag to enable split
status-bar functionality:

adb shell device_config put systemui qs_split_enabled true

To populate the view, you will also need to build and install an
experimental plugin from google3, coming shortly.

Test: manual
Change-Id: Iccf712a0355ebf8d9c6da2dac63874820270d405