I notice nios2mmu branch is only at 2.6.35. This means you are using the unstable branch?
Related question - the unstable branch appears to have no /arch/nios2/boards folder when I check it out, fresh, after an update. I can compile, but not run, using the Device Tree Wiki information. I assume some addresses are incorrect. I am able get an error message over the RS232 console. Do I need files in the .../boards folder - DTS_Generic perhaps? Any more (better) info here than the Device Tree wiki page? I am running (or trying to...) on a 2C35.
Thanks,