Pull up following revision(s) (requested by mrg in ticket #1851):

sys/arch/x86/include/specialreg.h: revision 1.207
sys/arch/x86/x86/errata.c: revision 1.31

x86: turn off zenbleed chicken bit on Zen2 cpus.

this is based upon Taylor's original work.  i just made the list
of CPUs to run on correct as i could determine.  (also, add some
Zen3 and Zen4 cpuids not yet used by any errata.)

(might be nice to have a better way to expression revision ranges
rather than specific cpuid matches, eg, 0x30-0x4f models in a cpu
family, etc.)

tested on ryzen 3600, and a ported zenbleed PoC that no longer
shows any obtained text.  (a similar module-version of it stopped
the PoC on a ryzen 3950x without having to reboot.)

https://www.amd.com/en/resources/product-security/bulletin/amd-sb-7008.html
https://lock.cmpxchg8b.com/zenbleed.html

(martin)