[sensors] Make generic_sensor a component

device/generic_sensor/public/cpp/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 source_set("cpp") {
   sources = [
+    "platform_sensor_configuration.cc",
+    "platform_sensor_configuration.h",
     "sensor_reading.cc",
     "sensor_reading.h",
   ]
 
+  defines = [ "DEVICE_GENERIC_SENSOR_IMPLEMENTATION" ]
+
   deps = [
     "//base",
     "//device/base/synchronization",
     "//device/generic_sensor/public/interfaces",
   ]
 }