kunit: configs: enable GPIO kunit test cases in all_tests.config

Enable CONFIG_GPIOLIB in all_tests.config to ensure the kunit test cases
for GPIO core can be built with this config.

Link: https://lore.kernel.org/r/20260629124245.27674-1-bartosz.golaszewski@oss.qualcomm.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: David Gow <david@davidgow.net>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>