nvmm - More hacks to maintain TSC mp synchronization between cpus

nvmm - More hacks to maintain TSC mp synchronization between cpus

* More hacks to try to discern whether qemu is actually trying to
  update the MSR_TSC in setstate or not.  Updating MSR_TSC completely
  blows up TSC mp synchronization.

  We assume qemu did not intend to update the TSC if it tries to write
  0 or tries to write the value returned in the previous getstate.

* This allows kernels to use the TSC as a clock, which costs nothing,
  verses the ACPI or HPET which have horrible overhead and a global
  mutex in qemu.