pylibfdt: Add stdint include to fix uint32_t

Some types used by libfdt.h are not understood the Python module since
they are defined outside it. An example is an attempt to do this:

   import libfdt
   result = libfdt.fdt_node_offset_by_phandle(fdt, phandle)

This results in:

TypeError: in method 'fdt_node_offset_by_phandle', argument 2 of
	type 'uint32_t'

Include the standard integer header file to fix this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>