dtoc: Bring in the libfdt module automatically

Use the same technique as with binman to load this module from the U-Boot
tree if available. This allows running tests without having to specify
the PYTHONPATH variable.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/test_fdt.py b/tools/dtoc/test_fdt.py
index d104f3c..d86fc86 100755
--- a/tools/dtoc/test_fdt.py
+++ b/tools/dtoc/test_fdt.py
@@ -16,6 +16,12 @@
 our_path = os.path.dirname(os.path.realpath(__file__))
 sys.path.insert(1, os.path.join(our_path, '..'))
 
+# Bring in the libfdt module
+sys.path.insert(2, 'scripts/dtc/pylibfdt')
+sys.path.insert(2, os.path.join(our_path, '../../scripts/dtc/pylibfdt'))
+sys.path.insert(2, os.path.join(our_path,
+                '../../build-sandbox_spl/scripts/dtc/pylibfdt'))
+
 from dtoc import fdt
 from dtoc import fdt_util
 from dtoc.fdt_util import fdt32_to_cpu