* Add a function to write to the relevant PLL register
* Break out the PLL configuration for the AR71XX into the CPU ops,
lifted from if_arge.c.
* Add the AR91XX PLL configuration ops, using the AR91XX register
definitions.
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.
