dtoc: Add tests

Add some tests of dtoc's functionality to make it easier to expand and
enhance the tool.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/dtoc_test_empty.dts b/tools/dtoc/dtoc_test_empty.dts
new file mode 100644
index 0000000..1e86655
--- /dev/null
+++ b/tools/dtoc/dtoc_test_empty.dts
@@ -0,0 +1,12 @@
+/*
+ * Test device tree file for dtoc
+ *
+ * Copyright 2017 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+ /dts-v1/;
+
+/ {
+};