dt-bindings: gpio: realtek-otto: Add rtl9310 compatible

Add the "realtek,rlt9310-gpio", "realtek,otto-gpio" compatible for GPIO
nodes on the RTL931x SoC series.

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