HWC/copybit : Add support to indicate driver on layer with Zorder 0

Some applications send RGBA layer with constant alpha 0xFF and
isOpaque=1. For these types of layer we don't get any wormHole
regions. Hence we see the previous content (framebuffer) due to
wrong selection of blending logic at kernel side.

To fix these kind of issues on MDP3 we make layer with Z order
zero as FG layer. This makes sure that proper blending logic
is chosen in kernel.

CRs-fixed: 521638
CRs-fixed: 517944
Change-Id: I172a46c3284916264a1413a6a16875afea2b1aad
diff --git a/libcopybit/copybit.h b/libcopybit/copybit.h
index 0f4332f..878eca4 100644
--- a/libcopybit/copybit.h
+++ b/libcopybit/copybit.h
@@ -77,6 +77,7 @@
     COPYBIT_FRAMEBUFFER_WIDTH = 7,
     /* FB height */
     COPYBIT_FRAMEBUFFER_HEIGHT = 8,
+    COPYBIT_FG_LAYER = 9,
 };
 
 /* values for copybit_set_parameter(COPYBIT_TRANSFORM) */