Allow config to disable battery percent setting

Respect config_battery_percentage_setting_available to determine whether
or not to allow showing battery percentage in the status bar.

Test: visual
Bug: 80129194
Change-Id: I23b0065ed99865a8df37c098b2f0f16d57799706
diff --git a/src/com/android/settings/display/BatteryPercentagePreferenceController.java b/src/com/android/settings/display/BatteryPercentagePreferenceController.java
index 4493158..be676e3 100644
--- a/src/com/android/settings/display/BatteryPercentagePreferenceController.java
+++ b/src/com/android/settings/display/BatteryPercentagePreferenceController.java
@@ -20,6 +20,7 @@
 import android.support.v7.preference.Preference;
 import android.support.v14.preference.SwitchPreference;
 
+import com.android.internal.R;
 import com.android.settings.core.PreferenceControllerMixin;
 import com.android.settingslib.core.AbstractPreferenceController;
 
@@ -40,7 +41,8 @@
 
     @Override
     public boolean isAvailable() {
-        return true;
+        return mContext.getResources()
+                .getBoolean(R.bool.config_battery_percentage_setting_available);
     }
 
     @Override