x86, hotplug: Handle retrigger irq by the first available CPU

The first cpu in irq cfg->domain is likely to be CPU 0 and may not be available
when CPU 0 is offline. Instead of using CPU 0 to handle retriggered irq, we use
first available CPU which is online and in this irq's domain.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1352835171-3958-13-git-send-email-fenghua.yu@intel.com


Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>