dt-bindings: pinctrl: mt2712: add binding document

The commit adds mt2712 compatible node in binding document.
Signed-off-by: NZhiyong Tao <zhiyong.tao@mediatek.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/pinctrl-mt65xx.txt

@@ -5,6 +5,7 @@ The Mediatek's Pin controller is used to control SoC pins.
 Required properties:
 - compatible: value should be one of the following.
 	"mediatek,mt2701-pinctrl", compatible with mt2701 pinctrl.
+	"mediatek,mt2712-pinctrl", compatible with mt2712 pinctrl.
 	"mediatek,mt6397-pinctrl", compatible with mt6397 pinctrl.
 	"mediatek,mt7623-pinctrl", compatible with mt7623 pinctrl.
 	"mediatek,mt8127-pinctrl", compatible with mt8127 pinctrl.