Implement using HPET timers and other mechanisms than TSC for time keeping

[axeld]

On CPUs that are able to change their frequency, the TSC increment is not invariant. Therefore, we cannot use it to compute time on these machines. Unfortunately, most recent CPUs are affected due to power saving features.

Furthermore, in a SMP environment, the TSC of the different CPUs can drift apart. See ​http://lkml.org/lkml/2005/11/4/173 for an interesting insight on that topic.

For HPET (and PM timer) see ACPI 3.0 specification ​http://www.acpi.info/spec.htm and ​http://www.intel.com/technology/architecture/hpetspec.htm