gpio: dt-bindings: add more loongson gpio chip support

This patch was to add loongson 2k0500, 2k2000 and 3a5000 gpio chip
dt-bindings support in yaml file.

Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

dt-bindings: gpio: add loongson gpio

Add the Loongson platform gpio binding with DT schema format using
json-schema.

Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>