dm: Add a more efficient libfdt library

Add a Python version of the libfdt library which contains enough features to
support the dtoc tool. This is only a very bare-bones implementation. It
requires the 'swig' to build.

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

lib/libfdt/test_libfdt.py

@@ -0,0 +1,14 @@
+#!/usr/bin/python
+
+import os
+import sys
+
+our_path = os.path.dirname(os.path.realpath(__file__))
+sys.path.append(os.path.join(our_path, '../../b/sandbox_spl/tools'))
+
+import libfdt
+
+with open('b/sandbox_spl/u-boot.dtb') as fd:
+    fdt = fd.read()
+
+print libfdt.fdt_path_offset(fdt, "/aliases")