This works well enough to bring a system up to single-user mode
using an MDROOT.
Known Issues:
* The EHCI USB doesn't currently work and will panic the kernel during
attach.
* The onboard ethernet won't work until the PLL routines have been
fleshed out and shoe-horned into if_arge.
* The WMAC device glue (and quite likely the if_ath support)
hasn't yet been implemented.
