gpio: ge: Replace GPLv2 boilerplate with SPDX

Replace the GPLv2 boilerplate text with a nice and short
SPDX header.

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>