doze: Make all features optional

This change makes all users of doze app declare supported sensors in
their device tree overlays.

Change-Id: I6444da1e8b42d0064a04981632c84f6c90ddaee7

doze/res/values/config.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+     Copyright (C) 2021 The LineageOS Project
+
+     Licensed under the Apache License, Version 2.0 (the "License"
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+<resources>
+    <!-- Sensor types -->
+    <string name="pickup_sensor_type"></string>
+    <string name="pocket_sensor_type"></string>
+</resources>