AudioSystem: refactor audio config cache and callbacks

Clean up implementation of audio configuration cache and
callback events from AudioFlinger:

- Define class AudioIoDescriptor for audio input and output
configurations outside of AudioSystem class.
- Do not use void * but an AudioIoDescriptor as argument to
audio config callbacks from AudioFlinger.
- Remove unused configuration events.
- Move AudioSystem audio input and output cache from static singletons to
members of AudioFlingerClient subclass.

Change-Id: I67c196c32c09ce2756af0755ee1fe631040c3270
diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index 9858b02..8e06138 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -543,7 +543,8 @@
               // no range check, doesn't check per-thread stream volume, AudioFlinger::mLock held
               float streamVolume_l(audio_stream_type_t stream) const
                                 { return mStreamTypes[stream].volume; }
-              void audioConfigChanged(int event, audio_io_handle_t ioHandle, const void *param2);
+              void ioConfigChanged(audio_io_config_event event,
+                                   const sp<AudioIoDescriptor>& ioDesc);
 
               // Allocate an audio_io_handle_t, session ID, effect ID, or audio_module_handle_t.
               // They all share the same ID space, but the namespaces are actually independent