Tidy up some code in the reference backend

Make some things private that don't need to be public in RefElementwiseWorkload.

Remove non-workload header files from RefWorkloads.hpp - the non-workload header
files are implementation detail of individual workloads, whereas RefWorloads.hpp
should only contain the workload definitions, needed for RefWorkloadFactory.

Signed-off-by: Matthew Bentham <matthew.bentham@arm.com>
Change-Id: I4c28963a027162a6560e56cf84b6c0063283e48f
diff --git a/src/backends/reference/workloads/RefElementwiseWorkload.hpp b/src/backends/reference/workloads/RefElementwiseWorkload.hpp
index 065a783..579e5de 100644
--- a/src/backends/reference/workloads/RefElementwiseWorkload.hpp
+++ b/src/backends/reference/workloads/RefElementwiseWorkload.hpp
@@ -21,15 +21,15 @@
 class RefElementwiseWorkload : public RefBaseWorkload<ParentDescriptor>
 {
 public:
-    using InType = typename ElementwiseBinaryFunction<Functor>::InType;
-    using OutType = typename ElementwiseBinaryFunction<Functor>::OutType;
-    using RefBaseWorkload<ParentDescriptor>::m_Data;
-
     RefElementwiseWorkload(const ParentDescriptor& descriptor, const WorkloadInfo& info);
     void Execute() const override;
     void ExecuteAsync(WorkingMemDescriptor& workingMemDescriptor)  override;
 
 private:
+    using InType = typename ElementwiseBinaryFunction<Functor>::InType;
+    using OutType = typename ElementwiseBinaryFunction<Functor>::OutType;
+    using RefBaseWorkload<ParentDescriptor>::m_Data;
+
     void Execute(std::vector<ITensorHandle*> inputs, std::vector<ITensorHandle*> outputs) const;
 };