dt-bindings: leds: aw2013: Document interrupt

AW2013 has an optional interrupt pin "INTN" which is used to report
completion of started operations (e.g. power up or LED breath effects).
The driver does not use it (yet) but it should be described for
completeness inside the DT schema.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Nikita Travkin <nikita@trvn.ru>
Link: https://lore.kernel.org/r/20230815-aw2013-vio-v3-1-2505296b0856@gerhold.net


Signed-off-by: Lee Jones <lee@kernel.org>