vmm/amd64: VM_SET_CPUID ioctl should refuse zero-entry non-legacy cpuid cfg

[rosenfeld_grumpf.hope-2000.org]

Summary

The kernel shouldn't accept a cpuid configuration that has no entries
without having the legacy flag set and just return EINVAL. A VCPU cpuid
configuration must either have zero cpuid entries and the legacy flag
set, or it must have the legacy flag clear and at least one cpuid entry.

[corvink]

This should be merged into the previous commit D51552 shouldn't it?

[rosenfeld_grumpf.hope-2000.org]

In D51553#1178181, @corvink wrote:

This should be merged into the previous commit D51552 shouldn't it?

Yes, eventually it will be.

It's currently a separate change as it fixes an issue in the illumos code in D51552, and as such will be submitted to illumos separately eventually.