[DeviceService] Move PowerMonitor interfaces, client lib, impl to live in Device Service

services/device/public/cpp/power_monitor/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.
 
 import("//build/config/features.gni")
 
-source_set("cpp") {
+source_set("power_monitor") {
   sources = [
     "power_monitor_broadcast_source.cc",
     "power_monitor_broadcast_source.h",
   ]
 
   deps = [
     "//base",
     "//mojo/public/cpp/bindings",
     "//services/service_manager/public/cpp",
   ]
 
   public_deps = [
-    "//device/power_monitor/public/interfaces",
+    "//services/device/public/interfaces",
   ]
 }