irqchip: armada-370-xp: Add suspend/resume support

This commit adds suspend/resume support to the irqchip driver used on
Armada XP platforms (amongst others). It does so by adding a set of
suspend/resume syscore_ops, that will respectively save and restore
the necessary registers to ensure interrupts continue to work after
resume.

It is worth mentioning that the affinity is lost during a
suspend/resume cycle, because when a secondary CPU is brought
off-line, all interrupts that are assigned to this CPU in terms of
affinity gets re-assigned to a still running CPU. Therefore, right
before entering suspend, all interrupts are assigned to the boot CPU.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: linux-kernel@vger.kernel.org
Link: https://lkml.kernel.org/r/1416585613-2113-4-git-send-email-thomas.petazzoni@free-electrons.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>