MP callouts

[Andrew Doran <ad%netbsd.org@localhost>]

Hi,

At the moment, callouts only fire on the boot CPU. The below diff allows for
callout processing on all CPUs, and for callouts to be bound to CPUs.

Each CPU has its own lock and call wheel. Non-MPSAFE callouts are always
run on the boot CPU, just in case there is an odd sync issue lurking
somewhere.

        http://www.netbsd.org/~ad/callout.diff

Any comments?

Thanks,
Andrew