dt-bindings: mfd: da9062: Move IRQ to optional properties

Move IRQ to optional properties, because the MFD DA9061/62
is usable without IRQ. This makes the chip usable for designs
that don't have the IRQ pin connected.

Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221122095833.3957-2-cniedermaier@dh-electronics.com