The full page verion of prevent ringing is still searchable.
- Created a new controller for parent entry.
- On the child controller, inherit the same getAvailabilityStatus() but
override AVILABLE_UNSEARCHABLE to AVAILABLE so it becomes searchable.
Fixes: 72748524
Test: existing robotests for PreventRingingPreferenceController
Change-Id: Id2454db110c81b59fa4a98338602b03de0812f8a
