dt-bindings: gpio: gpio_oxnas: remove obsolete bindings

Due to lack of maintenance and stall of development for a few years now,
and since no new features will ever be added upstream, remove the
OX810 and OX820 gpio bindings.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Daniel Golle <daniel@makrotopia.org>
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20230814-topic-oxnas-upstream-remove-v3-3-04a0c5cdda52@linaro.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Author: superna9999