IVGCVSW-8055 Add support for GELU activation function.

* Add support to CpuRef, CpuAcc and GpuAcc
* Add support to tflite parser, classic and opaque tflite delegates
* Add support to serializer and deserializer
* Add Unit tests

Signed-off-by: Teresa Charlin <teresa.charlinreyes@arm.com>
Change-Id: Ibc60ef2ef2a051e6d9af6e15d24c46316ec19de4
diff --git a/delegate/classic/src/Activation.hpp b/delegate/classic/src/Activation.hpp
index a93cee4..1c55c2e 100644
--- a/delegate/classic/src/Activation.hpp
+++ b/delegate/classic/src/Activation.hpp
@@ -109,6 +109,11 @@
             activationDesc.m_A = leakyReluParameters->alpha;
             break;
         }
+        case kTfLiteBuiltinGelu:
+        {
+            activationDesc.m_Function = armnn::ActivationFunction::Gelu;
+            break;
+        }
         default:
         {
             return kTfLiteError;