arm: dts: mt7623: add pinctrl nodes to the mt7623 dtsi file

Add pin controller node to the mt7623.dtsi file

Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>