IVGCVSW-1963: Add implementation classes for Cl, Neon and Ref backends

Change-Id: Ibb2efaf8b001a64a3f35eab2220990dc39889780
diff --git a/src/backends/reference/RefLayerSupport.hpp b/src/backends/reference/RefLayerSupport.hpp
index d29e956..e819b66 100644
--- a/src/backends/reference/RefLayerSupport.hpp
+++ b/src/backends/reference/RefLayerSupport.hpp
@@ -15,6 +15,11 @@
 namespace armnn
 {
 
+class RefLayerSupport : public ILayerSupport
+{
+    // TODO implement
+};
+
 bool IsActivationSupportedRef(const TensorInfo& input,
                               const TensorInfo& output,
                               const ActivationDescriptor& descriptor,