irqchip: renesas-irqc: Add wake-up support

The IRQC module clock is managed through Runtime PM and PM Domains.
If wake-up is enabled, this clock must not be disabled during system
suspend.

Hence implement irq_chip.irq_set_wake(), which increments/decrements the
clock's enable_count when needed.

This fixes wake-up by gpio-keys on r8a73a4/ape6evm.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Link: https://lkml.kernel.org/r/1427889606-18671-1-git-send-email-geert+renesas@glider.be
Signed-off-by: Jason Cooper <jason@lakedaemon.net>