Add common LED property - the function - to LED node.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220607102931.102805-8-krzysztof.kozlowski@linaro.org