reduce number of binder calls from mediaserver

Reduce the number of audio port, audio patch and
IO config changed binder calls from mediaserver to
client processes:
- Do not call IO config changed callback if selected
device is the same as previously selected one on a given
audio flinger playback or capture thread.
- Do not call the audio port or audo patch list update
callback on a client if this client as no listener registered.

Bug: 22045560.

Change-Id: If780e105404de79b7cb5c80c27b793ceb6b1c423
diff --git a/services/audioflinger/Threads.h b/services/audioflinger/Threads.h
index b12b091..0783371 100644
--- a/services/audioflinger/Threads.h
+++ b/services/audioflinger/Threads.h
@@ -436,6 +436,7 @@
                 bool                    mStandby;     // Whether thread is currently in standby.
                 audio_devices_t         mOutDevice;   // output device
                 audio_devices_t         mInDevice;    // input device
+                audio_devices_t         mPrevInDevice;    // previous input device
                 struct audio_patch      mPatch;
                 audio_source_t          mAudioSource;