gpio: gpio-xz: use the generic request/free implementations

gpio: gpio-xz: use the generic request/free implementations

Instead of storing in the chip data whether the chip uses pinctrl and
conditionally call pinctrl_{request,free}_gpio, just don't populate
request/free in that case.

This makes the implementations trivial and the same as the generic
implementations, thus we can just use them.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>