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/bsection.py b/tools/binman/bsection.py
index 650e9ba..e4c1900 100644
--- a/tools/binman/bsection.py
+++ b/tools/binman/bsection.py
@@ -24,6 +24,7 @@
 
     Attributes:
         _node: Node object that contains the section definition in device tree
+        _parent_section: Parent Section object which created this Section
         _size: Section size in bytes, or None if not known yet
         _align_size: Section size alignment, or None
         _pad_before: Number of bytes before the first entry starts. This
@@ -46,14 +47,16 @@
             section
         _entries: OrderedDict() of entries
     """
-    def __init__(self, name, node, test=False):
+    def __init__(self, name, parent_section, node, image, test=False):
         global entry
         global Entry
         import entry
         from entry import Entry
 
+        self._parent_section = parent_section
         self._name = name
         self._node = node
+        self._image = image
         self._offset = 0
         self._size = None
         self._align_size = None