mkamsboot: fix for newer fuzev2
These models are restricted to OF >= v02.3.31, probably because of a
hardware change
The OF checks a version string located between 0x0 and 0x200 in the
firmware block, so let's keep this part unmodified
We put our dualboot code at 0x200, and insert a branch + vectors at 0x0
That way our patched file will present the OF version to the fuzev2 OF
patching it, and we only waste 512 bytes on other models
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@27441 a1c6a512-1295-4272-9138-f99709370657