gpio: of: Switch to EXPORT_SYMBOL_GPL()

All exported functions provide genuine Linux-specific functionality.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20190906084539.21838-4-geert+renesas@glider.be


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>