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/test_fdt.py b/tools/dtoc/test_fdt.py
index 16a4430..028c8cb 100755
--- a/tools/dtoc/test_fdt.py
+++ b/tools/dtoc/test_fdt.py
@@ -449,6 +449,11 @@
         self.assertIn("node '/spl-test': Missing property 'one'",
                       str(e.exception))
 
+    def testGetFilename(self):
+        """Test the dtb filename can be provided"""
+        self.assertEqual(tools.GetOutputFilename('source.dtb'),
+                         self.dtb.GetFilename())
+
 
 class TestFdtUtil(unittest.TestCase):
     """Tests for the fdt_util module