irqchip: dw-apb-ictl: Always use use {readl|writel}_relaxed

irqchip: dw-apb-ictl: Always use use {readl|writel}_relaxed

There's no DMA at all, the device type memory attribute can ensure the
operations order and relaxed version imply compiler barrier, so we are safe
to use relaxed version to improve the performance a bit.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Link: https://lkml.kernel.org/r/1415773374-4629-2-git-send-email-jszhang@marvell.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>