Expand hypervisor probe.

- Bring over vmware probing code from tsc.c to identcpu.c and export
  hv_high.  Rename vm_vendor to hv_vendor.
- Add VM_GUEST_VMWARE and let tsc.c just check that instead of probing.
- Restore old SMBIOS strings as a fallback.
Flesh out print_hv_info().