KVM: selftests: Refactor kvm_cpuid_has() to prep for X86_PROPERTY_* support

Refactor kvm_cpuid_has() to prepare for extending X86_PROPERTY_* support
to KVM as well as "this CPU".

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221006005125.680782-6-seanjc@google.com