Move the ACPI PM timer emulation into vmm.ko.

This reduces variability during timer calibration by keeping the emulation
"close" to the guest. Additionally having all timer emulations in the kernel
will ease the transition to a per-VM clock source (as opposed to using the
host's uptime keep track of time).

Discussed with:	grehan


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273683 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f