amd64: be more precise when enabling the AlderLake small core PCID workaround

In particular, do not enable the workaround if INVPCID is not supported
by the core.

Reported by: "Chen, Alvin W" <Weike.Chen@Dell.com>
Reviewed by: markj
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D37940