cooperative multitasking

[Aaron Durbin]

Hi,

I just uploaded some patches that implement the ability to
cooperatively multitask on the boot cpu. The patches still need some
cleaning up, but I wanted to start the conversation. Fwiw, Ron claims
he needs this. So blame him. This notion does allow for people to
write state machines using the callbacks and can still rely on
synchronous programming.

Patches are here:
remote:   http://review.coreboot.org/3191
remote:   http://review.coreboot.org/3192
remote:   http://review.coreboot.org/3193

-Aaron