genirq: Add irqchip_set_wake_parent

This proves to be useful with stacked domains, when the current
domain doesn't implement wake-up, but expect the parent to do so.

Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Link: https://lkml.kernel.org/r/1426088629-15377-2-git-send-email-marc.zyngier@arm.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>