binman: Obtain the list of device trees from the config

We always have a device tree for U-Boot proper. But we may also have one
for SPL and TPL. Add a new Entry method to find out what DTs an entry
has, and use that list when updating DTs.

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

tools/binman/bsection.py

@@ -8,6 +8,7 @@
 from __future__ import print_function
 
 from collections import OrderedDict
+from sets import Set
 import sys
 
 import fdt_util
@@ -92,6 +93,13 @@ class Section(object):
             entry.SetPrefix(self._name_prefix)
             self._entries[node.name] = entry
 
+    def GetFdtSet(self):
+        """Get the set of device tree files used by this image"""
+        fdt_set = Set()
+        for entry in self._entries.values():
+            fdt_set.update(entry.GetFdtSet())
+        return fdt_set
+
     def SetOffset(self, offset):
         self._offset = offset