- use _MAXNCPU instead of 4
- convert xpmsg_lock from a simplelock to a kmutex
- don't wait for sparc_noop IPI calls
- remove xmpsg_func's "retval" parameter and usage
- remove the IPI at high IPL message
- rework cpu_attach() a bunch, refactoring calls to getcpuinfo() and setting
  of cpi, and split most of the non-boot CPU handling into a new function
- make CPU_INFO_FOREACH() work whether modular or not
- move the MP cpu_info pages earlier
- move a few things in cpu.c around to colsolidate the MP code together
- remove useless if (cpus == NULL) tests -- cpus is an array now

with these changes, and an additional change to crazyintr() to not printf(),
i can get to single user shell on my SS20 again.  i can run a fwe commands
but some of them cause hangs.  "ps auxw" works, but "top -b" does not.

tested in UP LOCKDEBUG/DEBUG/DIAGNOSTIC kernel as well.
MP kernel with only cpu0 configured panics starting /sbin/init.
have not yet tested on a real UP machine.

(mrg)