Switch to per-CPU PMC results, and completely rewrite the pmc(1) tool. Now
the PMCs are system-wide, fine-grained and more tunable by the user.

We don't do application tracking, since it would require to store the PMC
values in mdproc and starting/stopping the counters on each context switch.
While this doesn't seem to be particularly difficult to achieve, I don't
think it is really interesting; and if someone really wants to measure
the performance of an application, they can simply schedctl it to a cpu
and look at the PMC results for this cpu.

Note that several options are implemented but not yet used.

(maxv)