This patch depends on the (uncommitted) work done in
https://reviews.freebsd.org/D11801 to actually produce a result on a Zen
system.
Works fine on my Sandybridge laptop (boot -v):
```
Package ID shift: 4
L3 cache ID shift: 4
L2 cache ID shift: 1
L1 cache ID shift: 1
Core ID shift: 1
FreeBSD/SMP: Multiprocessor System Detected: 4 CPUs
FreeBSD/SMP: 1 package(s) x 2 core(s) x 2 hardware threads
```
(This matches prior behavior.)