Ring & notif vol missing on a largescreen device

Before:
"Ring & notification volume" showed up in volume panel and in volume
settings.

Now (what prompted this bugreport):
A device config was changed to mark it not voice capable.
"Ring & notification volume" disappeared from both places;
"Notification volume" showed up only in volume settings, not panel.

Fix: the voice capable should not be a factor when determining
availability for ring/notification slices.

After this fix is applied:
"Ring & notification volume" to reappear at both settings and panel.

Bug: 256548882

Test: make DEBUG_ROBOLECTRIC=1 ROBOTEST_FILTER="VolumePanelTest|RingVolumePreferenceControllerTest|NotificationVolumePreferenceControllerTest|SeparateRingVolumePreferenceController" RunSettingsRoboTests -j40

Change-Id: Ie2b1913bde6a64303c4d9fde3724889f949c363b