gpio: 74xx-mmio: use new generic GPIO chip API

Convert the driver to using the new generic GPIO chip interfaces from
linux/gpio/generic.h.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250702-gpio-mmio-rework-v2-7-6b77aab684d8@linaro.org


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