local_apics are allocated sequentially and never removed, so
we can stop any iterations that go to MAX_APICS as soon as we
hit the first NULL. Looking at a small guest running a virtio-net
workload with oprofile, this drops apic_get_delivery_bitmask()
from #3 in the profile to down in the noise.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>