cpu: provide a wakeup mechanism that can be used to pull CPUs out of sleep.

cpu: provide a wakeup mechanism that can be used to pull CPUs out of sleep.
Make interrupts use the new wakeup method, and pull all of the interrupt
stuff into the cpu base class so that only the wakeup code needs to be updated.
I tried to make wakeup, wakeCPU, and the various other mechanisms for waking
and sleeping a little more sane, but I couldn't understand why the statistics
were changing the way they were.  Maybe we'll try again some day.