The csky,mpintc could deliver a external irq to one cpu or all cpus, but
it couldn't deliver a external irq to a group of cpus with cpu_mask. So
we only use auto deliver mode when affinity mask_val is equal to
cpu_present_mask.

There is no limitation for only two cpus in SMP system.
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>