audio policy: refactor HW audio sources

Refactor management of hardware audio sources to make use of
ClientDescriptor class:
- HW sources are now tracked by port ID and not audio patch handle.
- startAudioSource() and stopAudioSource() APIs are updated to use
audio_port_handle_t as source identifier.
- AudioSourceDescriptor class is deleted and replaced by
SourceClientDescriptor class deriving from TrackClientDescriptor

Test: make.
Change-Id: Ie418b566519a591f036b538a77319f8e30aa99a8
diff --git a/services/audiopolicy/AudioPolicyInterface.h b/services/audiopolicy/AudioPolicyInterface.h
index c9e99d5..d4c49d9 100644
--- a/services/audiopolicy/AudioPolicyInterface.h
+++ b/services/audiopolicy/AudioPolicyInterface.h
@@ -226,9 +226,9 @@
 
     virtual status_t startAudioSource(const struct audio_port_config *source,
                                       const audio_attributes_t *attributes,
-                                      audio_patch_handle_t *handle,
+                                      audio_port_handle_t *portId,
                                       uid_t uid) = 0;
-    virtual status_t stopAudioSource(audio_patch_handle_t handle) = 0;
+    virtual status_t stopAudioSource(audio_port_handle_t portId) = 0;
 
     virtual status_t setMasterMono(bool mono) = 0;
     virtual status_t getMasterMono(bool *mono) = 0;