binman: Add a function to obtain the image for an Entry

At present we have an 'image' property in the entry for this purpose, but
this is not necessary and seems error-prone in the presence of
inheritance. Add a function instead. The Entry_section class overrides
this with a special version, since top-level sections are in fact images,
since Image inherits Entry_section.

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

tools/binman/image.py

@@ -42,7 +42,6 @@ class Image(section.Entry_section):
             we create a section manually.
     """
     def __init__(self, name, node, test=False):
-        self.image = self
         section.Entry_section.__init__(self, None, 'section', node, test)
         self.name = 'main-section'
         self.image_name = name