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.
Reviewed by: emaste
Tested by: emaste, mike tancsa <firstname.lastname@example.org>, Stefan Hegnauer <email@example.com>
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D34367