hal: add support for hfp on auto platform

Add auto platform specific pcm device id and
playback volume control to support hfp with
dual asm loopback.

Change-Id: I6bd2ae63c8733dd770f48c1b2557c4d3d5a6b101
diff --git a/hal/Android.mk b/hal/Android.mk
index 7a0c69f..4411134 100644
--- a/hal/Android.mk
+++ b/hal/Android.mk
@@ -65,6 +65,10 @@
 endif
 endif
 
+ifeq ($(TARGET_BOARD_AUTO),true)
+  LOCAL_CFLAGS += -DPLATFORM_AUTO
+endif
+
 LOCAL_CFLAGS += -Wno-macro-redefined
 
 LOCAL_HEADER_LIBRARIES := libhardware_headers