gpio: rcar: Enable mask on suspend

Now when lazy interrupt disable has been enabled in the driver
then extend the code to set IRQCHIP_MASK_ON_SUSPEND which tells
the core that only IRQs marked as wakeups need to stay enabled
during Suspend-to-RAM.

Tested on the Lager board with GPIO-keys and Suspend-to-RAM.

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>