audio policy: use factory to create audio policy manager

Use the class factory to create the audio policy mamager
instead of AudioPolicyManager class constructor and
use a pointer to an AudioPolicyInterface.

Change-Id: Ibb5a8eee5d597db67cf13f279c909181cfee9949
diff --git a/services/audiopolicy/AudioPolicyService.h b/services/audiopolicy/AudioPolicyService.h
index 40f589b..66d9cad 100644
--- a/services/audiopolicy/AudioPolicyService.h
+++ b/services/audiopolicy/AudioPolicyService.h
@@ -539,7 +539,7 @@
     sp<AudioCommandThread> mOutputCommandThread;    // process stop and release output
     struct audio_policy_device *mpAudioPolicyDev;
     struct audio_policy *mpAudioPolicy;
-    AudioPolicyManager *mAudioPolicyManager;
+    AudioPolicyInterface *mAudioPolicyManager;
     AudioPolicyClient *mAudioPolicyClient;
 
     KeyedVector< audio_source_t, InputSourceDesc* > mInputSources;