backends/reference: Add ReduceSum operation support

This patch addes ReduceSum operation support for reference backend,
which computes the sum of elements across dimensions of a tensor.

Changelog v1:
- Fix file header descriptions.

Chagelog v2:
- Fix line limit issue.
- Fix type conversion issue.

Changelog v3:
- Remove tabs.
- Modify newly added file headers.

Changelog v4:
- Symbol on header isn't allowed so drop it from newly added file headers.

Changelog v5:
- Remove tabs, fix the use of brackets and align lines correctly.

Changelog v6:
- Add serializer and deserializer support.

Changelog v7:
- Fix build error add missed code.

Changelog v8:
- Rename ReduceSumDecriptor to ReduceDescriptor
    - Update m_KeepDims field data type to bool on ReduceDescriptor
    - Add ReduceOperation field to ReduceDescriptor

- Rename ReduceSumLayer to ReduceLayer
    - Update ReduceLayer to use ReduceDescriptor
    - Update ReduceLayer::ValidateTensorShapesFromInputs() function

- Rename RefReduceSumWokload to RefReduceWorkload
    - Update workload to use ReduceDescriptor
    - Update workload to use Decoders and Encoders

- Remove ReduceSum.hpp and ReduceSum.cpp
- Added Reduce.hpp and Reduce.cpp
     - Move Mean.cpp (which is implementing REDUCE_MEAN) functionality to Reduce.cpp
     - Update RefMeanWorkload to call Reduce function with ReduceOperation::Mean argument

- Remove Mean.hpp and Mean.cpp
- Update the Serializer/Deserializer ArmnnSchema.fbs for ReduceLayer, ReduceDescriptor, and ReduceOperation
- Update Serializer and Deserializer for serializing/parsing ReduceLayer
- Added TfLiter parser Sum test for REDUCE_SUM operator
- Make corresponding changes on front-end and Ref backend to support REDUCE_SUM operator

Changelog v9:
- Fixed build errors.

Change-Id: I8c8e034f3df73f9565b3c18eff51ecca6c542195
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Sadik Armagan <sadik.armagan@arm.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b071bf0..789e2d9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -368,6 +368,8 @@
     src/armnn/layers/PreluLayer.cpp
     src/armnn/layers/RankLayer.hpp
     src/armnn/layers/RankLayer.cpp
+    src/armnn/layers/ReduceLayer.hpp
+    src/armnn/layers/ReduceLayer.cpp
     src/armnn/layers/ReshapeLayer.hpp
     src/armnn/layers/ReshapeLayer.cpp
     src/armnn/layers/ResizeLayer.hpp
@@ -829,6 +831,7 @@
              src/armnnTfLiteParser/test/Squeeze.cpp
              src/armnnTfLiteParser/test/StridedSlice.cpp
              src/armnnTfLiteParser/test/Sub.cpp
+             src/armnnTfLiteParser/test/Sum.cpp
              src/armnnTfLiteParser/test/TransposeConv.cpp
              src/armnnTfLiteParser/test/Transpose.cpp
              src/armnnTfLiteParser/test/Unpack.cpp
@@ -925,6 +928,7 @@
             src/armnnDeserializer/test/DeserializePermute.cpp
             src/armnnDeserializer/test/DeserializePooling2d.cpp
             src/armnnDeserializer/test/DeserializeRank.cpp
+            src/armnnDeserializer/test/DeserializeReduceSum.cpp
             src/armnnDeserializer/test/DeserializeReshape.cpp
             src/armnnDeserializer/test/DeserializeResizeBilinear.cpp
             src/armnnDeserializer/test/DeserializeRsqrt.cpp