gpio: Kconfig: make GPIO_SYSFS config always visible

To reduce boot time, we have disabled CONFIG_EXPERT and CONFIG_DEBUG_KERNEL in seco-mx6 defconfig: seco-ne/yocto/layers/meta-seconorth-machine!507 (merged)

However, for backward compatibility, we need to leave CONFIG_GPIO_SYSFS enabled. For this, the config should be visible even when expert mode is disabled.