uma: fix zone domain overlaying pcpu cache with disabled cpus

[rlibby]

Summary

UMA zone structures have two arrays at the end which are sized according
to the machine: an array of cpu count length, and an array of NUMA
domain count length. The CPU counting was wrong in the case where some
CPUs are disabled (when mp_ncpus != mp_maxid + 1), and this caused the
second array to be overlaid with the first.

Reported by: olivier

Test Plan

Disable some CPUs. Olivier did this with

machdep.hyperthreading_allowed="0"

but I did not have a hyperthreading machine to test so I did this from
the loader:

set hint.lapic.1.disabled=1
set hint.lapic.3.disabled=1
set hint.lapic.5.disabled=1
set hint.lapic.7.disabled=1
set hint.lapic.9.disabled=1
set hint.lapic.11.disabled=1
set hint.lapic.13.disabled=1
set hint.lapic.15.disabled=1

Then:
kyua test -k /usr/tests/sys/Kyuafile

[jeff]

mea culpa. Can you commit to 12.x as well?

[rlibby]

In D23318#511196, @jeff wrote:

mea culpa. Can you commit to 12.x as well?

Will do.