IVGCVSW-3013 Add unit tests for QSymm16 LSTM

* Add unit tests for QSymm16 LSTM
* Update supportedTypes in WorkloadData & RefLayerSupport with
  DataType::QuantisedSymm16

Change-Id: I1a2627b11b707d68d7d7002f63b985f9571ee177
Signed-off-by: Conor Kennedy <conor.kennedy@arm.com>
diff --git a/src/backends/reference/RefLayerSupport.cpp b/src/backends/reference/RefLayerSupport.cpp
index 67c13c3..8eded84 100644
--- a/src/backends/reference/RefLayerSupport.cpp
+++ b/src/backends/reference/RefLayerSupport.cpp
@@ -616,7 +616,8 @@
     bool supported = true;
 
     std::array<DataType,2> supportedTypes = {
-        DataType::Float32
+        DataType::Float32,
+        DataType::QuantisedSymm16
     };
 
     supported &= CheckSupportRule(TypeAnyOf(input, supportedTypes), reasonIfUnsupported,