dt-bindings: pinctrl: add external interrupt support to MT7622 pinctrl

Extend the capability of MT7622 pinctrl with adding EINT so that each
GPIO can be used to notify CPU when a signal state is changing on the
line as an external interrupt.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/pinctrl-mt7622.txt

@@ -9,6 +9,16 @@ Required properties for the root node:
  - #gpio-cells: Should be two. The first cell is the pin number and the
    second is the GPIO flags.
 
+Optional properties:
+- interrupt-controller  : Marks the device node as an interrupt controller
+
+If the property interrupt-controller is defined, following property is required
+- reg-names: A string describing the "reg" entries. Must contain "eint".
+- interrupts : The interrupt output from the controller.
+- #interrupt-cells: Should be two.
+- interrupt-parent: Phandle of the interrupt parent to which the external
+  GPIO interrupts are forwarded to.
+
 Please refer to pinctrl-bindings.txt in this directory for details of the
 common pinctrl bindings used by client devices, including the meaning of the
 phrase "pin configuration node".