dt-bindings: leds: Mention GPIO triggers

dt-bindings: leds: Mention GPIO triggers

We reuse the trigger-sources phandle to just point to
GPIOs we may want to use as LED triggers.

Example:

gpio: gpio@0 {
    compatible "my-gpio";
    gpio-controller;
    #gpio-cells = <2>;
    interrupt-controller;
    #interrupt-cells = <2>;
    #trigger-source-cells = <2>;
};

leds {
    compatible = "gpio-leds";
    led-my-gpio {
        label = "device:blue:myled";
        gpios = <&gpio 0 GPIO_ACTIVE_HIGH>;
        default-state = "off";
        linux,default-trigger = "gpio";
        trigger-sources = <&gpio 1 GPIO_ACTIVE_HIGH>;
    };
};

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230926-gpio-led-trigger-dt-v2-2-e06e458b788e@linaro.org
Signed-off-by: Lee Jones <lee@kernel.org>