IVGCVSW-6626 Promote backend headers in backendCommon to  armnn/backends

Move the following header files from backendsCommon to armnn/backends.

* MemCopyWorkload.hpp
* TensorHandle.hpp
* Workload.hpp
* WorkloadData.hpp
* WorkloadFactory.hpp

Replace them with forwarding headers and a pragma deprecation message.
Resolve the deprecation messages in Arm NN code.

Signed-off-by: Colm Donelan <colm.donelan@arm.com>
Change-Id: I47f116b30f86e478c9057795bc518c391a8ae514
diff --git a/src/backends/reference/workloads/LstmUtils.hpp b/src/backends/reference/workloads/LstmUtils.hpp
index 11fbb77..7f06012 100644
--- a/src/backends/reference/workloads/LstmUtils.hpp
+++ b/src/backends/reference/workloads/LstmUtils.hpp
@@ -6,7 +6,7 @@
 #pragma once
 
 #include "BaseIterator.hpp"
-#include <backendsCommon/TensorHandle.hpp>
+#include <armnn/backends/TensorHandle.hpp>
 
 // Helper functions ported from the Android code base
 // Refer to: android/external/tensorflow/tensorflow/contrib/lite/kernels/internal/reference/portable_tensor_utils.cc