hal: enable audio over display port

Add support for audio over display port.

Change-Id: I3480d89c61ee5e5983715ec943fb02b1a9d5d151
diff --git a/hal/Android.mk b/hal/Android.mk
index 705e5e8..812ed99 100644
--- a/hal/Android.mk
+++ b/hal/Android.mk
@@ -310,6 +310,10 @@
     LOCAL_SHARED_LIBRARIES += libperipheral_client
 endif
 
+ifeq ($(strip $(AUDIO_FEATURE_ENABLED_DISPLAY_PORT)),true)
+    LOCAL_CFLAGS += -DDISPLAY_PORT_ENABLED
+endif
+
 LOCAL_CFLAGS += -Wall -Werror
 
 LOCAL_COPY_HEADERS_TO   := mm-audio