i386: kvm: x2apic is not supported without in-kernel irqchip

This is necessary so that x2apic is not improperly enabled when the
in-kernel irqchip is disabled.

This won't generate a warning with "-cpu ...,check" because the current
check/enforce code is broken (it checks the host CPU data directly,
instead of using kvm_arch_get_supported_cpuid()), but it will be
eventually fixed to properly report the missing x2apic flag.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
