x86: ignore stepping for APL30 errata

The issue is present in all apollolake cpus and it doesn't look like
there'll be a fix in the future.

See
https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/pentium-celeron-n-series-j-series-datasheet-spec-update.pdf

MFC after: 1 week
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D37621