genirq: explicitly mask a freed irq

When an interrupt is freed, the shutdown or the disable callback
is called for that interrupt. These calls might not be implemented
or even if they were, might not mask the interrupt.

Explicitly mask the interrupt when it is freed. If not masked, the
interrupt could trigger, set the pending bit in the irq controller
and cause unnecessary wakeup or exits from idle power collapse.

Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>

Conflicts:

	kernel/irq/manage.c