hal: update audio feature flags

- update audio feature flags to use
  AUDIO_FEATURE_ENABLED_XXX instead of
  AUDIO_FEATURE_DISABLED_XXX.
- These feature flags are defined
  by target board config file

Change-Id: Iba482d8b72bfa2675877d833d7abcb93d4cf4907
diff --git a/post_proc/Android.mk b/post_proc/Android.mk
index c50b7d0..97002fa 100644
--- a/post_proc/Android.mk
+++ b/post_proc/Android.mk
@@ -3,7 +3,7 @@
 
 include $(CLEAR_VARS)
 
-ifneq ($(strip $(AUDIO_FEATURE_DISABLED_PROXY_DEVICE)),true)
+ifeq ($(strip $(AUDIO_FEATURE_ENABLED_PROXY_DEVICE)),true)
     LOCAL_CFLAGS += -DAFE_PROXY_ENABLED
 endif