vkernel - Clock optimizations, pre-zero 'ram'.

vkernel - Clock optimizations, pre-zero 'ram'.

* The vkernel now defaults to using an imprecise (host-tick-resolution)
  timer.

* The vkernel now pre-faults all of its 'system' memory at startup in order
  to avoid dynamically faulting it in after it has gone MP (which creates
  a lot of contention on the host machine).