MIPS: mscc: ocelot: add interrupt controller properties to GPIO controller

The GPIO controller also serves as an interrupt controller for events
on the GPIO it handles.

An interrupt occurs whenever a GPIO line has changed.

Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20015/
Cc: robh+dt@kernel.org
Cc: mark.rutland@arm.com
Cc: ralf@linux-mips.org
Cc: jhogan@kernel.org
Cc: linux-gpio@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: thomas.petazzoni@bootlin.com