pinctrl: sunxi: select GPIOLIB

Allwinner pin controllers are also GPIO controllers.

Currently, if GPIOLIB is forgot to be chosen, the build of
pinctrl-sunxi.c will fail for lacking a lot of gpiochip_* functions.

Select GPIOLIB to ensure this driver can be built.

Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>