binman: Allow reading an entry from an image

It is useful to be able to extract entry contents from an image to see
what is inside. Add a simple function to read the contents of an entry,
decompressing it by default.

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

tools/binman/image.py

@@ -82,7 +82,9 @@ class Image(section.Entry_section):
         dtb.Scan()
 
         # Return an Image with the associated nodes
-        return Image('image', dtb.GetRoot())
+        image = Image('image', dtb.GetRoot())
+        image._data = data
+        return image
 
     def Raise(self, msg):
         """Convenience function to raise an error referencing an image"""