x86: Probe the TSC frequency earlier

This lets us use the TSC to implement early DELAY, limiting the use of
the sometimes-unreliable 8254 PIT.

PR: 262155
Reviewed by: emaste
Tested by: emaste, mike tancsa <mike@sentex.net>, Stefan Hegnauer <stefan.hegnauer@gmx.ch>
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D34367