dtoc: update dtb_platdata to support cd-gpios

Currently dtoc does not support the property cd-gpios used to declare
the gpios for card detect in mmc.

This patch adds support to cd-gpios property.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/test_dtoc.py b/tools/dtoc/test_dtoc.py
index 209542c..67ca9a8 100755
--- a/tools/dtoc/test_dtoc.py
+++ b/tools/dtoc/test_dtoc.py
@@ -485,7 +485,7 @@
         output = tools.GetOutputFilename('output')
         with self.assertRaises(ValueError) as e:
             self.run_test(['struct'], dtb_file, output)
-        self.assertIn("Node 'phandle-target' has no '#clock-cells' property",
+        self.assertIn("Node 'phandle-target' has no cells property",
                       str(e.exception))
 
     def test_aliases(self):