OF: pinctrl: MIPS: lantiq: implement lantiq/xway pinctrl support

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.

Signed-off-by: John Crispin <blogic@openwrt.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Cc: devicetree-discuss@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org