Add audio stream and usage for virtual assistant

New stream type: AUDIO_STREAM_ASSISTANT
This is intended to be used by a virtual assistant like
Google Assistant, Bixby, etc.

The audio stream has own volume alias and the volume
does not change by volume changes of other streams.

Bug: 123745215
Test: make
Change-Id: I17ec0480cad4c3507a97454ccb832255adda9897
Merged-In: I17ec0480cad4c3507a97454ccb832255adda9897
Signed-off-by: Baekgyeong Kim <baek.kim@samsung.com>
diff --git a/services/audiopolicy/service/AudioPolicyEffects.cpp b/services/audiopolicy/service/AudioPolicyEffects.cpp
index 4947714..60caa31 100644
--- a/services/audiopolicy/service/AudioPolicyEffects.cpp
+++ b/services/audiopolicy/service/AudioPolicyEffects.cpp
@@ -562,7 +562,8 @@
     AUDIO_STREAM_BLUETOOTH_SCO_TAG,
     AUDIO_STREAM_ENFORCED_AUDIBLE_TAG,
     AUDIO_STREAM_DTMF_TAG,
-    AUDIO_STREAM_TTS_TAG
+    AUDIO_STREAM_TTS_TAG,
+    AUDIO_STREAM_ASSISTANT_TAG
 };
 
 // returns the audio_stream_t enum corresponding to the output stream name or