pinctrl/lantiq: Fix GPIO Setup of GPIO Port3

Some special handling of GPIO Port 3 is needed because of
some hardware thingofabob.

Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Martin Schiller <mschiller@tdt.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>