binman: Record the parent section of each section

At present sections have no record of their parent so it is not possible
to traverse up the tree to the root and figure out the position of a
section within the image.

Change the constructor to record this information.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/image.py b/tools/binman/image.py
index 4b922b5..e113a60 100644
--- a/tools/binman/image.py
+++ b/tools/binman/image.py
@@ -42,7 +42,8 @@
         self._size = None
         self._filename = '%s.bin' % self._name
         if test:
-            self._section = bsection.Section('main-section', self._node, True)
+            self._section = bsection.Section('main-section', None, self._node,
+                                             self, True)
         else:
             self._ReadNode()
 
@@ -52,7 +53,7 @@
         filename = fdt_util.GetString(self._node, 'filename')
         if filename:
             self._filename = filename
-        self._section = bsection.Section('main-section', self._node)
+        self._section = bsection.Section('main-section', None, self._node, self)
 
     def GetFdtSet(self):
         """Get the set of device tree files used by this image"""