IVGCVSW-1898 : Ref backend folder structure

* Reference backend is renamed to backends/reference as per
  https://confluence.arm.com/display/MLENG/Pluggable+backends

Change-Id: I27a13c274eb60995dfb459e3c49c0e2f60bcd32c
diff --git a/src/backends/reference/backend.cmake b/src/backends/reference/backend.cmake
new file mode 100644
index 0000000..95e72a4
--- /dev/null
+++ b/src/backends/reference/backend.cmake
@@ -0,0 +1,7 @@
+#
+# Copyright © 2017 Arm Ltd. All rights reserved.
+# SPDX-License-Identifier: MIT
+#
+
+add_subdirectory(${PROJECT_SOURCE_DIR}/src/backends/reference)
+list(APPEND armnnLibraries armnnRefBackend armnnRefBackendWorkloads)