Settings: Add volume link notification switch

Change-Id: I06027bc4f13c8a60b19a2b7ded73ce76da4e4f02

Tablets don't need to link volumes they don't have

This feature broke the notification volume slider in settings for
devices without telephony service (tablets) and isn't applicable
anyways since they don't have ringtone volume streams.

Change-Id: Ifff10ecd35b53f5fc08a36332814fb00d20b4350

Settings: Fix linked volume crash + inconsistent state

- Ensure we fetch from Secure, not System
- Don't initialize every time we toggle
- Set the checkbox state from Settings value since
  the preference assumes a default of 0

CYNGNOS-1638

Change-Id: Ia519cef2295a6b6083b2b168f4c16df78f423cee