genirq: Honour IRQ's affinity hint during migration

An IRQ affinity is broken during hotplug/isolation when there
are no online and un-isolated CPUs in the current affinity mask.
An online and un-isolated CPU from the irq_default_affinity mask
(i.e /proc/irq/default_smp_affinity) is used as the current
affinity. However Individual IRQs can have their affinity hint
set via irq_set_affinity_hint() API. When such hint is available,
use it instead of the irq_default_affinity which is a system level
setting.

Change-Id: I53a537582ec4e1aed0c59b49f4fd5b6ca7c0c332
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>