hal: Support for usb audio features

Added support for usb audio feature and
related proxy device support

Change-Id: Ia64e9eff20fbbada6f08795686cdbc0ba462bafb
diff --git a/hal/Android.mk b/hal/Android.mk
index 5f5c7ae..b4527bf 100644
--- a/hal/Android.mk
+++ b/hal/Android.mk
@@ -34,6 +34,11 @@
     LOCAL_SRC_FILES += audio_extn/fm.c
 endif
 
+ifneq ($(strip $(AUDIO_FEATURE_DISABLED_USBAUDIO)),true)
+    LOCAL_CFLAGS += -DUSB_HEADSET_ENABLED
+    LOCAL_SRC_FILES += audio_extn/usb.c
+endif
+
 LOCAL_SHARED_LIBRARIES := \
 	liblog \
 	libcutils \