hal: Added support for HFP

 - Added setparameter to be set from hfp app to enable
   and disable hfp session.
 - Implemeted start and stop hfp session which takes
   care of switching device and setting the session

Change-Id: Ie8697328ccbfee09d0d162f6fad01ddb552e4f83
diff --git a/hal/Android.mk b/hal/Android.mk
index 86f92d9..d8a4733 100644
--- a/hal/Android.mk
+++ b/hal/Android.mk
@@ -47,6 +47,10 @@
     LOCAL_CFLAGS += -DUSB_HEADSET_ENABLED
     LOCAL_SRC_FILES += audio_extn/usb.c
 endif
+ifneq ($(strip $(AUDIO_FEATURE_DISABLED_HFP)),true)
+    LOCAL_CFLAGS += -DHFP_ENABLED
+    LOCAL_SRC_FILES += audio_extn/hfp.c
+endif
 
 ifneq ($(strip $(AUDIO_FEATURE_DISABLED_SSR)),true)
     LOCAL_CFLAGS += -DSSR_ENABLED