gpio: rcar: Prevent module clock disable when wake-up is enabled

When the GPIO module is needed for wake-up, it's module clock must not
be disabled. Hence implement irq_chip.irq_set_wake(), which
increments/decrements the clock's enable_count when needed, and forwards
the wake-up state to the upstream interrupt controller.

This fixes wake-up from s2ram using gpio-keys when using a PM Domain to
manage the module clock.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>