binman: Update state when replacing device-tree entries

Since the state module holds references to all the device trees used by
binman, it must be updated when the device trees are updated. Add support
for this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/fdt.py b/tools/dtoc/fdt.py
index cd7673c..6770be7 100644
--- a/tools/dtoc/fdt.py
+++ b/tools/dtoc/fdt.py
@@ -695,6 +695,14 @@
         node = Node(fdt, parent, offset, name, path)
         return node
 
+    def GetFilename(self):
+        """Get the filename of the device tree
+
+        Returns:
+            String filename
+        """
+        return self._fname
+
 def FdtScan(fname):
     """Returns a new Fdt object"""
     dtb = Fdt(fname)