binman: Allow faked blobs in blob-ext-list

Since this is a list of blobs, each blob should have the ability to be
faked, as with blob-ext. Update the Entry base class to set allow_fake
and use the base class in the section code also, so that this propagagtes
to blob-ext-list, which is not a section.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/entry.py b/tools/binman/entry.py
index bac90bb..e4a1f2d 100644
--- a/tools/binman/entry.py
+++ b/tools/binman/entry.py
@@ -960,7 +960,7 @@
         Args:
             allow_fake: True if allowed, False if not allowed
         """
-        pass
+        self.allow_fake = allow_fake
 
     def CheckMissing(self, missing_list):
         """Check if any entries in this section have missing external blobs