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/entry.py

@@ -18,6 +18,7 @@ except:
     have_importlib = False
 
 import os
+from sets import Set
 import sys
 
 import fdt_util
@@ -164,6 +165,20 @@ class Entry(object):
     def GetDefaultFilename(self):
         return None
 
+    def GetFdtSet(self):
+        """Get the set of device trees used by this entry
+
+        Returns:
+            Set containing the filename from this entry, if it is a .dtb, else
+            an empty set
+        """
+        fname = self.GetDefaultFilename()
+        # It would be better to use isinstance(self, Entry_blob_dtb) here but
+        # we cannot access Entry_blob_dtb
+        if fname and fname.endswith('.dtb'):
+            return Set([fname])
+        return Set()
+
     def AddMissingProperties(self):
         """Add new properties to the device tree as needed for this entry"""
         for prop in ['offset', 'size', 'image-pos']: