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/src/backends/reference/RefLayerSupport.cpp b/src/backends/reference/RefLayerSupport.cpp
index 25334c3..7d5c3b5 100644
--- a/src/backends/reference/RefLayerSupport.cpp
+++ b/src/backends/reference/RefLayerSupport.cpp
@@ -109,6 +109,7 @@
                 case ActivationFunction::Abs:
                 case ActivationFunction::BoundedReLu:
                 case ActivationFunction::Elu:
+                case ActivationFunction::HardSwish:
                 case ActivationFunction::LeakyReLu:
                 case ActivationFunction::Linear:
                 case ActivationFunction::ReLu: