hwc: Add binder interface to get the visibleRegion

- This binder interface can be used by clients to know the
  active visible region for a display(pri/ext/virt)
- When external orientation is used, return the destFrame of
  the FrameBuffer layer, as its the viewFrame

Change-Id: I7cfd149c76c16b9a3031103c89b1932d44bcbecd
diff --git a/libhwcomposer/hwc_fbupdate.cpp b/libhwcomposer/hwc_fbupdate.cpp
index 0ca5ad9..d601f8f 100644
--- a/libhwcomposer/hwc_fbupdate.cpp
+++ b/libhwcomposer/hwc_fbupdate.cpp
@@ -176,6 +176,8 @@
         }
         calcExtDisplayPosition(ctx, NULL, mDpy, sourceCrop, displayFrame,
                                    transform, orient);
+        //Store the displayFrame, will be used in getDisplayViewFrame
+        ctx->dpyAttr[mDpy].mDstRect = displayFrame;
         setMdpFlags(layer, mdpFlags, 0, transform);
         // For External use rotator if there is a rotation value set
         ret = preRotateExtDisplay(ctx, layer, info,