arm64: dts: mediatek: mt6795-xperia-m5: Add display backlight support

Add the relevant nodes for display backlight on Sony Xperia M5: this
needs both the SoC PWM IP and MT6332 PMIC LED strings.

Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230721082822.680010-3-angelogioacchino.delregno@collabora.com


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