gpio: ge: Enable COMPILE_TEST for the driver

Driver is so simple, yet there was a room for mistakes.
Reduce their appearance in the future by enabling COMPILE_TEST
option.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>