OF: pinctrl: MIPS: lantiq: implement lantiq/xway pinctrl support
Implement support for pinctrl on lantiq/xway socs. The IO core found on these
socs has the registers for pinctrl, pinconf and gpio mixed up in the same
register range. As the gpio_chip handling is only a few lines, the driver also
implements the gpio functionality. This obseletes the old gpio driver that was
located in the arch/ folder.