binman: Tidy up the vblock entry

At present if there are two vblock entries an image their contents are
written to the same file in the output directory. This prevents checking
the contents of each separately.

Fix this by adding part of the entry path to the filename, and add some
missing comments.

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

tools/binman/entry.py

@@ -456,3 +456,21 @@ features to produce new behaviours.
         if missing:
             raise ValueError('Documentation is missing for modules: %s' %
                              ', '.join(missing))
+
+    def GetUniqueName(self):
+        """Get a unique name for a node
+
+        Returns:
+            String containing a unique name for a node, consisting of the name
+            of all ancestors (starting from within the 'binman' node) separated
+            by a dot ('.'). This can be useful for generating unique filesnames
+            in the output directory.
+        """
+        name = self.name
+        node = self._node
+        while node.parent:
+            node = node.parent
+            if node.name == 'binman':
+                break
+            name = '%s.%s' % (node.name, name)
+        return name