arm64: dts: mediatek: mt8173-elm: Add backlight enable pin config

Add the proper pinctrl for GPIO95 backlight enable pin and assign it
to the pwm-backlight node.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20211102144224.457446-2-angelogioacchino.delregno@collabora.com


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