KVM: ioapic/msi interrupt delivery consolidation

ioapic_deliver() and kvm_set_msi() have code duplication. Move
the code into ioapic_deliver_entry() function and call it from
both places.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>