hal: add support to separate headset and headphones mixer backend

add backend apply support for voice headphone path

Test: local build
Bug: 112827678
Change-Id: I819ad66a657b2c2e6b86025bf506b37377c45cf5
Signed-off-by: yixuanjiang <yixuanjiang@google.com>
diff --git a/hal/msm8960/platform.h b/hal/msm8960/platform.h
index b0bd98a..d2bcd0c 100644
--- a/hal/msm8960/platform.h
+++ b/hal/msm8960/platform.h
@@ -44,6 +44,7 @@
     SND_DEVICE_OUT_SPEAKER_AND_HEADPHONES,
     SND_DEVICE_OUT_VOICE_SPEAKER,
     SND_DEVICE_OUT_VOICE_HEADPHONES,
+    SND_DEVICE_OUT_VOICE_HEADSET,
     SND_DEVICE_OUT_HDMI,
     SND_DEVICE_OUT_SPEAKER_AND_HDMI,
     SND_DEVICE_OUT_BT_SCO,