Always calculate divisor for the counter mode of LAPIC timer. Even if
initially configured in the TSC deadline mode, eventtimer subsystem
can be switched to periodic, and then DCR register is loaded with
unitialized value.

Reset the LAPIC eventtimer frequency and min/max periods when changing
between deadline and counted periodic modes.

Reported and tested by: Vladimir Zakharov <zakharov.vv@gmail.com>
Sponsored by: The FreeBSD Foundation