The panel_flag property was used in ChromeOS's downstream kernel. It was
used to signal whether the downstream device was a fixed panel or
a connector for an external display.

This property was dropped in favor of standard OF graph descrptions of
downstream display panels and bridges.

Drop the property from the device tree file.

Fixes: cabc71b0 ("arm64: dts: mt8183: Add kukui-jacuzzi-damu board")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20231130074032.913511-2-wenst@chromium.orgSigned-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>