pc: Require IRQ remapping and EIM if there could be x2APIC CPUs

It would prevent starting guest with incorrect configs
where interrupts couldn't be delivered to CPUs with
APIC IDs > 255.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
