Bluetooth: Use AsyncFdWatcher for power management

Implement low power mode using timeouts from the interface.

Test: Boots, Bluetooth turns on/off,
      Instrumented bt_vendor library shows power management
      calls.
Change-Id: Ic4fcbb222f24b66c13f3797b14475d278c49fbc6
diff --git a/bluetooth/1.0/default/vendor_interface.h b/bluetooth/1.0/default/vendor_interface.h
index 79611cd..ce5769c 100644
--- a/bluetooth/1.0/default/vendor_interface.h
+++ b/bluetooth/1.0/default/vendor_interface.h
@@ -53,6 +53,8 @@
             PacketReadCallback packet_read_cb);
   void Close();
 
+  void OnTimeout();
+
   void OnDataReady(int fd);
 
   void *lib_handle_;