An interface was added to derive an implied TSC frequency from pvclock
in 2015, but this interface was never exposed anywhere user-visible.
Reviewed by: kib, bryanv
Differential Revision: https://reviews.freebsd.org/D32974
Add support for the KVM paravirtual clock device.
Sponsored by: Juniper Networks, Inc.
Sponsored by: Klara, Inc.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D29733