hal: Enable USB RX and Handset Mic combination support for Voice call

-For voice call usecase if connected USB OUT device does not have a
mic, currently we fallback to Earpiece-Handset mic device pair.
-With tunnel mode USB support, we can instead use USB RX and
Handset Mic as a device pair for the voice call.
-Update device selection to ensure that this pair is selected.

Change-Id: I0fc6c990bef91d675ea5f2bf13b3ed0b576db9ee
diff --git a/hal/msm8916/platform.h b/hal/msm8916/platform.h
index 24c793e..b91c501 100644
--- a/hal/msm8916/platform.h
+++ b/hal/msm8916/platform.h
@@ -117,6 +117,7 @@
     SND_DEVICE_OUT_VOICE_TX,
     SND_DEVICE_OUT_AFE_PROXY,
     SND_DEVICE_OUT_USB_HEADSET,
+    SND_DEVICE_OUT_USB_HEADPHONES,
     SND_DEVICE_OUT_SPEAKER_AND_USB_HEADSET,
     SND_DEVICE_OUT_TRANSMISSION_FM,
     SND_DEVICE_OUT_ANC_HEADSET,