Audio Effect API: process reverse stream function

Added function to audio effect interface for processing of
a reverse stream.
This is necessary for audio pre processes like echo cancellation.

Change-Id: I6e12d79dbbed6376acdfc79304b8c0ab3f705eae
diff --git a/media/libeffects/visualizer/EffectVisualizer.cpp b/media/libeffects/visualizer/EffectVisualizer.cpp
index aeebd4d..3c3af8f 100644
--- a/media/libeffects/visualizer/EffectVisualizer.cpp
+++ b/media/libeffects/visualizer/EffectVisualizer.cpp
@@ -450,7 +450,8 @@
 const struct effect_interface_s gVisualizerInterface = {
         Visualizer_process,
         Visualizer_command,
-        Visualizer_getDescriptor
+        Visualizer_getDescriptor,
+        NULL,
 };