dtoc: Update fdt tests to increase code coverage

At present only some of the fdt functionality is tested. Add more tests to
cover the rest of it. Also turn on test coverage, which is now 100% with
a small exclusion for a Python 3 feature.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/dtoc_test_simple.dts b/tools/dtoc/dtoc_test_simple.dts
index 895cc1f..165680b 100644
--- a/tools/dtoc/dtoc_test_simple.dts
+++ b/tools/dtoc/dtoc_test_simple.dts
@@ -21,6 +21,7 @@
 		longbytearray = [09 0a 0b 0c 0d 0e 0f 10 11];
 		stringval = "message";
 		stringarray = "multi-word", "message";
+		notstring = [20 21 22 10 00];
 	};
 
 	spl-test2 {