WIP: AR91XX (and AR724X, maybe) support

[Adrian Chadd]

> http://people.freebsd.org/~adrian/rspro/ar91xx-support.1.diff

I'm going to commit the AR71XX specific bits and the CPU ops tonight.
I can then convert over the bits of the codebase that needs CPU
specific bits (WB prodding, USB setup, device enable/disable) without
breaking the tree.

I'll then commit the AR91XX and part of the AR724X support once I've
rewritten the GPL bits.



Adrian