Make the CPU width a macro

[andrew]

Summary

This allows us to increase it later when 1000 core machines are
available. For now make it 3 digits to support the current > 99 core
machines.

[bz]

usr.sbin/pmcstat/pmcstat.c

123

This may sound weird, but how far are we off from 4 digits? I understand that in academia 1088 core RISC-V exists...

123

also PMC_CPU_STR_WIDTH as it CPU_WIDTH could easily be confused with 32 vs. 64 vs. 128 bit?

[emaste]

usr.sbin/pmcstat/pmcstat.c

123

Not too far; I expect to have 768 in my office shortly and will almost certainly have > 1000 during 15.x's lifetime. But committing this as a NFC first (with the macro staying at 3) makes sense to me.