irqchip: dw-apb-ictl: Add PM support

This patch adds in support for S2R for dw-apb-ictl irqchip driver.

We can used relaxed variants in the resume hook because there's no DMA
at all here, the device type memory attribute can ensure the operations
order and relaxed version imply compiler barrier.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Link: https://lkml.kernel.org/r/1415773374-4629-4-git-send-email-jszhang@marvell.com


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