libfdt: Add new headers and defines

The libfdt overlay support introduces a bunch of new includes and
functions.

Make sure we are able to build it by adding the needed glue.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Simon Glass <sjg@chromium.org>

include/libfdt_env.h

@@ -23,6 +23,12 @@ typedef __be64 fdt64_t;
 #define fdt64_to_cpu(x)		be64_to_cpu(x)
 #define cpu_to_fdt64(x)		cpu_to_be64(x)
 
+#ifdef __UBOOT__
+#include <vsprintf.h>
+
+#define strtoul(cp, endp, base)	simple_strtoul(cp, endp, base)
+#endif
+
 /* adding a ramdisk needs 0x44 bytes in version 2008.10 */
 #define FDT_RAMDISK_OVERHEAD	0x80