dm: Add a header that provides access to the of-platdata structs

This header can be included from anywhere, but will only pull in the
of-platdata struct definitions when this feature is enabled (and only in
SPL).

Signed-off-by: Simon Glass <sjg@chromium.org>

include/dt-structs.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2016 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __DT_STTUCTS
+#define __DT_STTUCTS
+
+/* These structures may only be used in SPL */
+#if CONFIG_IS_ENABLED(OF_PLATDATA)
+struct phandle_2_cell {
+	const void *node;
+	int id;
+};
+#include <generated/dt-structs.h>
+#endif
+
+#endif