Settings: Display 'Calls' category on non-voice devices.

Since the category applies to any call, include config for
this interruption even on non-voice-capable devices.

Bug: 17666139
Change-Id: I3732246179c527220f8c6bee539ba7bc1e80de18

res/xml/zen_mode_settings.xml

@@ -37,8 +37,8 @@
             android:switchTextOn="" />
 
         <SwitchPreference
-            android:key="phone_calls"
-            android:title="@string/zen_mode_phone_calls"
+            android:key="calls"
+            android:title="@string/zen_mode_calls"
             android:persistent="false"
             android:switchTextOff=""
             android:switchTextOn="" />