gpio: GPIO_GRGPIO should depend on OF

gpio: GPIO_GRGPIO should depend on OF

While the Aeroflex Gaisler GRGPIO driver has no build-time dependency on
gpiolib-of, it supports only DT-based configuration, and is used only on
DT systems.  Hence add a dependency on OF, to prevent asking the user
about this driver when configuring a kernel without DT support.

Fixes: bc40668def384256 ("gpio: grgpio: drop Kconfig dependency on OF_GPIO")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Link: https://lore.kernel.org/r/db6da3d11bf850d89f199e5c740d8f133e38078d.1738760539.git.geert+renesas@glider.be
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>