hwc: Add assertive display support.

Add assertive display support to hwc. This feature takes effect when
node /sys/class/graphics/fb*/ad is present. This signifies that that LM0
is being used with fb* for writeback.

When a video playback begins we write "1" to this node to indicate to
post processing that a writeback will happen. Likewise a "0" is written
to this node when playback stops.

The original contents are worked upon and the modified output is fed
via writeback to either rotator or mdp as appropriate.

The feature doesnt trigger when either:
1) Buffer size exceeds 2048
2) External display is connected
3) Multiple yuv streams are present

When this mode is active, MDP comp is applied only to yuv layer.

Change-Id: If5520f9dc849de3189c9f9ed4e9072c8f8f760e1

libhwcomposer/hwc.cpp

@@ -36,6 +36,7 @@
 #include "hwc_dump_layers.h"
 #include "external.h"
 #include "hwc_copybit.h"
+#include "hwc_ad.h"
 #include "profiler.h"
 
 using namespace qhwc;
@@ -107,6 +108,8 @@ static void reset(hwc_context_t *ctx, int numDisplays,
         if(ctx->mCopyBit[i])
             ctx->mCopyBit[i]->reset();
     }
+
+    ctx->mAD->reset();
 }
 
 //clear prev layer prop flags and realloc for current frame