hal: compilation fix for extended feature flags

- Fix compilation error for offload, Dolby,
  HDMI pass through, FLAC decoder, and hardware
  accelerated effects when extended feature
  flags are disabled.

Change-Id: If64d5fa5d124b42d40d7e123b887db8e0a5d7426
diff --git a/post_proc/Android.mk b/post_proc/Android.mk
index be70166..ed46f17 100644
--- a/post_proc/Android.mk
+++ b/post_proc/Android.mk
@@ -14,8 +14,12 @@
 	virtualizer.c \
 	reverb.c \
 	effect_api.c \
-	effect_util.c \
-        hw_accelerator.c
+	effect_util.c
+
+ifeq ($(strip $(AUDIO_FEATURE_ENABLED_HW_ACCELERATED_EFFECTS)),true)
+    LOCAL_CFLAGS += -DHW_ACCELERATED_EFFECTS
+    LOCAL_SRC_FILES += hw_accelerator.c
+endif
 
 LOCAL_CFLAGS+= -O2 -fvisibility=hidden