sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

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

x86: Perform late TSC calibration before LAPIC timer calibration

This ensures that LAPIC calibration is done using the correct tsc_freq
value, i.e., the one associated with the TSC timecounter. It does mean
though that TSC calibration cannot use sbinuptime() to read the
reference timecounter, as timehands are not yet set up.

Reviewed by: kib, jhb
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D33209

x86: Defer LAPIC calibration until after timecounters are available

This ensures that we have a good reference timecounter for performing
calibration.

Change lapic_setup to avoid configuring the timer when booting, and move
calibration and initial configuration to a new lapic routine,
lapic_calibrate_timer. This calibration will be initiated from
cpu_initclocks(), before an eventtimer is selected.

Reviewed by: kib, jhb
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D33206

x86: Deduplicate clock.h

The headers were mostly identical on amd64 and i386.

No functional change intended.

Reviewed by: cperciva, mav, imp, kib, jhb
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D33205