kvm_arch_get_supported_cpuid checks for global cpuid restrictions, it
does not require any CPUState reference. Changing its interface allows
to call it before any VCPU is initialized.

CC: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>