dt-bindings: pinctrl: pinctrl-microchip-sgpio: Add irq support

This describe the new bindings for the added IRQ support in the
pinctrl-microchip-sgpio driver.

Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201209142753.683208-3-lars.povlsen@microchip.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>