Introduce rbutil/mkzenboot, a replacement for tools/mkzenboot

The old tools/mkzenboot has a number of problems: very hard to maintain,
poor integration with rbutil. Restart from scratch by recycling all the
crypto and descrambling code, rewrite the actual firmware modification part
to handle all scenarios in a much clearer way. The code is ready to be
integrated into Rockbox Utility, by using the very similar interface to
mkimxboot.
I copied all the keys from the old mkzenboot, so it can potentially support
the older Creative ports, but since this is untested, I prefer not do so
at the moment. However, I did add a "mixed" boot option to support the
dualboot style used in the older ports.

Change-Id: I80cfc48fa78187baa1b1692e8a30ec7137cea37b

rbutil/mkzenboot/dualboot/config.h

@@ -0,0 +1,22 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2013 by Amaury Pouly
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+
+/** empty, used by register files */