IVGCVSW-4440 : Add HARD_SWISH Support to Activation in CpuRef

* Add a new Activiation type of HardSwish.
* Add CpuRef support and tests.

Signed-off-by: Colm Donelan <Colm.Donelan@arm.com>
Change-Id: I68c3840aa45b7a27d5e416a5d50fe8f99f003ce8
diff --git a/include/armnn/Types.hpp b/include/armnn/Types.hpp
index b00a8bf..d66a1fd 100644
--- a/include/armnn/Types.hpp
+++ b/include/armnn/Types.hpp
@@ -57,13 +57,14 @@
     TanH        = 1,
     Linear      = 2,
     ReLu        = 3,
-    BoundedReLu = 4, ///< min(a, max(b, input))
+    BoundedReLu = 4, ///< min(a, max(b, input)) ReLu1 & ReLu6.
     SoftReLu    = 5,
     LeakyReLu   = 6,
     Abs         = 7,
     Sqrt        = 8,
     Square      = 9,
-    Elu         = 10
+    Elu         = 10,
+    HardSwish   = 11
 };
 
 enum class ArgMinMaxFunction