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
Sponsored by: The FreeBSD Foundation

(cherry picked from commit 62d09b46ad7508ae74d462e49234f0a80f91ff69)