gpio: loongson: fixup the warning about OF_GPIO direct dependencies

WARNING: unmet direct dependencies detected for OF_GPIO
  Depends on [n]: GPIOLIB [=y] && OF [=n] && HAS_IOMEM [=y]
  Selected by [y]:
  - GPIO_LOONGSON_64BIT [=y] && GPIOLIB [=y] && HAS_IOMEM [=y] && (LOONGARCH || COMPILE_TEST [=y])

Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202303091728.UUe6LWye-lkp@intel.com


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