hwc: Implement idle-fallback for videos

In case of videos, do a fallback using 2 pipes per mixer at most.
This redraw will happen only once to reduce pipes from at most 4
to at most 2 and never draw again until there is an update.

Change-Id: I78c0dc2af4e3bd7e9128994e507e777187b4e247
diff --git a/libhwcomposer/hwc.cpp b/libhwcomposer/hwc.cpp
index 9dcb439..bf997ee 100644
--- a/libhwcomposer/hwc.cpp
+++ b/libhwcomposer/hwc.cpp
@@ -235,7 +235,6 @@
 
     ctx->mOverlay->configDone();
     ctx->mRotMgr->configDone();
-    MDPComp::resetIdleFallBack();
 
     return ret;
 }
@@ -501,6 +500,7 @@
     // This is only indicative of how many times SurfaceFlinger posts
     // frames to the display.
     CALC_FPS();
+    MDPComp::resetIdleFallBack();
     return ret;
 }