sysutils/devcpu-data: Permit neither vendor option to be chosen

This allows users with both AMD- and Intel-based systems to build and
install devcpu-data-amd and devcpu-data-intel, but not force either to
be installed with pkg install devcpu-data.

PR: 259883
Reported by: Martin Birgmeier <d8zNeCFG@aon.at>
Approved by: sbruno (maintainer)

Differential Revision: https://reviews.freebsd.org/D33036