Add two states for ringer view model.

This CL adds a control over the availability of ringer drawer in volume
dialog. It handles the unsupported current ringer mode and the single
volume mode cases.

Flag: com.android.systemui.volume_redesign
Bug: 369993851
Test: atest SystemUiRoboTests:VolumeDialogRingerDrawerViewModelTest
Change-Id: I02dff77b7d3c98ede32cdc3af25d0443f0381dd6