Fix a few CPUID emulation issues:

Fix a few CPUID emulation issues:

Don't advertise a hyperthreaded CPU. This doesn't make a lot of sense now
as we only provide UP guest support. This, combined with the other CPUID
issues fixed, fooled NetBSD's topology enumeration code into thinking we
had an unsupportable core/thread/package configuration.

Also fixed the unsupported CPUID functions by returning 0 in the return
registers instead of leaving whatever trash happened to be there before
the call was made.