arm64: dts: mediatek: asurada: Add display backlight

Add the display backlight for the Asurada platform. It relies on the
display PWM controller, so also enable and configure this component.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Link: https://lore.kernel.org/r/20221102190611.283546-3-nfraprado@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>