This allows a KVM guest to get an accurate cycle counter without having to do a VM exit, which happens when either HPET or ACPI is used.
KVMCLOCK quality is set to 2000 to ensure it is preferred, when it is available. Otherwise, if it was set to 1000, both TSC and KVMCLOCK could be detected and TSC will most likely get selected over KVMCLOCK, based on probe order.
KVM clock also supports getting the wall clock time but that is not implemented yet.
This change is dependent on D16305 being committed first.