gpiolib: Kill unused GPIOF_EXPORT and Co

There is no use of the GPIOF_EXPORT in the kernel. Kill it for good.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>