Enable time zone preference on wifi-only device.

When auto time zone preference is not available, it should be considered
disabled, so that user can still select time zone.

Change-Id: I9b17205a11ff512da02694e3bce06cfbd21dd7db
Fix: 34203177
Test: make RunSettingsRoboTests

src/com/android/settings/datetime/AutoTimeZonePreferenceController.java

@@ -67,7 +67,7 @@ public class AutoTimeZonePreferenceController extends PreferenceController
     }
 
     public boolean isEnabled() {
-        return Settings.Global.getInt(mContext.getContentResolver(),
+        return isAvailable() && Settings.Global.getInt(mContext.getContentResolver(),
                 Settings.Global.AUTO_TIME_ZONE, 0) > 0;
     }
 }