binman: Add support for a collection of entries

The vblock entry type includes code to collect the data from a number of
other entries (not necessarily subentries) and concatenating it. This is
a useful feature for other entry types.

Make it a base class, so that vblock can use it, along with other entry
types.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/entry.py b/tools/binman/entry.py
index ac25986..a157038 100644
--- a/tools/binman/entry.py
+++ b/tools/binman/entry.py
@@ -438,6 +438,11 @@
         """Convenience function to raise an error referencing a node"""
         raise ValueError("Node '%s': %s" % (self._node.path, msg))
 
+    def Info(self, msg):
+        """Convenience function to log info referencing a node"""
+        tag = "Info '%s'" % self._node.path
+        tout.Detail('%30s: %s' % (tag, msg))
+
     def Detail(self, msg):
         """Convenience function to log detail referencing a node"""
         tag = "Node '%s'" % self._node.path