IVGCVSW-2095 Add reference implementation and unit tests for SpaceToBatchNd

Change-Id: I27ffebdece6e68460931a44c15b9b029f9fce638
diff --git a/src/backends/reference/backend.mk b/src/backends/reference/backend.mk
index 007efce..cc8c24f 100644
--- a/src/backends/reference/backend.mk
+++ b/src/backends/reference/backend.mk
@@ -54,9 +54,11 @@
         workloads/RefResizeBilinearUint8Workload.cpp \
         workloads/RefSoftmaxFloat32Workload.cpp \
         workloads/RefSoftmaxUint8Workload.cpp \
+        workloads/RefSpaceToBatchNdWorkload.cpp \
         workloads/RefSplitterFloat32Workload.cpp \
         workloads/RefSplitterUint8Workload.cpp \
         workloads/ResizeBilinear.cpp \
+        workloads/SpaceToBatchNd.cpp \
         workloads/Softmax.cpp
 
 # BACKEND_TEST_SOURCES contains the list of files to be included