Update logic for disabling the PCI module.

Summary:
FreeBSD on ThunderX2 does support PCI, and apparently the KCM
even works. https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=234256

Reviewers: davidedmundson

Reviewed By: davidedmundson

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D17785