dt-bindings: gpio: Convert lantiq,gpio-mm-lantiq to DT schema

Convert the Lantiq SoC External Bus memory mapped GPIO binding to DT
schema format. It's a straight forward conversion.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20250714202837.3011521-1-robh@kernel.org


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>