o Do not use a special struct to keep track of CPUs we found;
instead, use struct pcpu. This handles all the magic WRT
thread creation (yay!).
o Respect MAXCPU.
o Use the vhpt_base and vhpt_size values to initialize the AP.
o Style fixes.
Note that this commit temporarily breaks SMP configurations.
Previously APs didn't do anything, but they now enter the
scheduler. They hold sched_lock for more than 5 secs though
and cause a panic. That's what I call progress :-)
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