x86: Perform late TSC calibration before LAPIC timer calibration

[markj]

Summary

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.

[kib]

sys/x86/x86/tsc.c

718

Perhaps add a comment explaining why do you directly use tc_get_timecount(), instead of only saying it in the commit message.

[markj]

Explain why we read the timecounter directly.