gpio: grgpio: drop Kconfig dependency on OF_GPIO

This driver has no build-time dependency on gpiolib-of so remove the
Kconfig switch.

Link: https://lore.kernel.org/r/20241015131832.44678-1-brgl@bgdev.pl


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