dt-bindings: gpio: realtek-otto: Add rtl9300 compatible

Add the "realtek,rlt9300-gpio", "realtek,otto-gpio" compatible for GPIO
nodes on the RTL930x SoC series. This SoC requires an extra register
range, defining the interrupt CPU mapping registers.

Signed-off-by: Sander Vanheule <sander@svanheule.net>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>