dt-bindings: counter: add interrupt-counter binding

Add binding for the interrupt counter node

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210301080401.22190-2-o.rempel@pengutronix.de
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>