Add and configure WLED node to enable backlight
control on WLED-enabled devices.

Signed-off-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Link: https://lore.kernel.org/r/20210228130831.203765-10-konrad.dybcio@somainline.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>