apic_common: migrate missing fields

This patch adds missed sipi_vector and wait_for_sipi fields to a new
subsection of the vmstate of the apic_common module. Saving and loading
of these fields makes migration of the apic state deterministic.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
[Initialize the field in pre_load and kvm_apic_realize. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
