Punched out a version of the microblaze on a ZYBO dev board, which required
a few tweaks an additions to run on real hardware.
Refactored the qemu and zybo microblaze target.
The qemu target has 128KB of ram at 0 and the rest at 0x90000000.
Split the binary so that the vector table lives at 0 and everything else in
the high address.