Implement a hook of KVM_SET_CPUID2 for additional consistency check.
Intel TDX or AMD SEV has a restriction on the value of cpuid. For example,
some values must be the same between all vcpus. Check if the new values
are consistent with the old values. The check is light because the cpuid
consistency is very model specific and complicated. The user space VMM
should set cpuid and MSRs consistently.
The x86 backend should check the consistency of KVM_SET_CPUID2 because it
has its constraint. Add a callback for it. The backend code will come as
another patch.
TDX doesn't support APICV, inhibit APICv for TDX guest. Follow how SEV
does it. Define a new inhibit reason for TDX, set it on TD
initialization, and add the flag to kvm_x86_ops.required_apicv_inhibits.
