IVGCVSW-1804 : Add Subtraction layer types and placeholders

Change-Id: Ib9a477e5ce590df74ba05fece77258b9204f6523
diff --git a/src/armnn/backends/test/IsLayerSupportedTestImpl.hpp b/src/armnn/backends/test/IsLayerSupportedTestImpl.hpp
index a580be3..7745972 100644
--- a/src/armnn/backends/test/IsLayerSupportedTestImpl.hpp
+++ b/src/armnn/backends/test/IsLayerSupportedTestImpl.hpp
@@ -350,7 +350,7 @@
 
 DECLARE_LAYER_POLICY_2_PARAM(Splitter)
 
-
+DECLARE_LAYER_POLICY_1_PARAM(Subtraction)
 
 
 // Generic implementation to get the number of input slots for a given layer type;