arm64: dts: mediatek: mt8395-nio-12l: Prepare MIPI DSI port

arm64: dts: mediatek: mt8395-nio-12l: Prepare MIPI DSI port

This board can use a MIPI-DSI panel on the DSI0 connector: in
preparation for adding an overlay for the Radxa Display 8HD,
add the backlight, and some definitions for pins available
through the DSI0 port.

Signed-off-by: Julien Massot <julien.massot@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20250304-radxa-panel-overlay-v2-1-3ee6797d3f86@collabora.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>