x86: ioapic: Add the smp configuration to ioapic unittest

Adds -smp configuration for ioapic unittest. This is essentially
required to test IOAPIC Logical destination mode, where we send
an interrupt to more than one vcpus at the same time.

Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>