IVGCVSW-4386 Add ArmNN reference support for QAsymmS8

 * Added Quantization Scheme for QAsymmS8
 * Added Unit Tests for QAsymmS8
 * Renamed QAsymm8 calls to QAsymmU8

Signed-off-by: Ryan OShea <Ryan.OShea2@arm.com>
Change-Id: I897b4e018ba1d808cc3f8c113f2be2dbad49c8db
diff --git a/src/backends/reference/workloads/Encoders.hpp b/src/backends/reference/workloads/Encoders.hpp
index 8ddd559..f522976 100644
--- a/src/backends/reference/workloads/Encoders.hpp
+++ b/src/backends/reference/workloads/Encoders.hpp
@@ -32,6 +32,13 @@
                 params.first);
         }
         ARMNN_NO_DEPRECATE_WARN_END
+        case armnn::DataType::QAsymmS8:
+        {
+            return std::make_unique<QASymmS8Encoder>(
+                static_cast<int8_t*>(data),
+                info.GetQuantizationScale(),
+                info.GetQuantizationOffset());
+        }
         case armnn::DataType::QAsymmU8:
         {
             return std::make_unique<QASymm8Encoder>(