binman: Add support for flashrom FMAP

Add an entry which can hold an FMAP region as used by flashrom, an
open-source flashing tool used on Linux x86 machines. This provides a
simplified non-hierarchical view of the entries in the image and has a
signature at the start to allow flashrom to find it in the image.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/entry.py b/tools/binman/entry.py
index dc09b81..8b910fe 100644
--- a/tools/binman/entry.py
+++ b/tools/binman/entry.py
@@ -361,6 +361,15 @@
         """
         self.WriteMapLine(fd, indent, self.name, self.offset, self.size)
 
+    def GetEntries(self):
+        """Return a list of entries contained by this entry
+
+        Returns:
+            List of entries, or None if none. A normal entry has no entries
+                within it so will return None
+        """
+        return None
+
     def GetArg(self, name, datatype=str):
         """Get the value of an entry argument or device-tree-node property