KVM: x86: Software disabled APIC should still deliver NMIs

Currently, the APIC logical map does not consider VCPUs whose local-apic is
software-disabled.  However, NMIs, INIT, etc. should still be delivered to such
VCPUs. Therefore, the APIC mode should first be determined, and then the map,
considering all VCPUs should be constructed.

To address this issue, first find the APIC mode, and only then construct the
logical map.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>