arm64: dts: exynos: Remove the OF graph from DSI node

The OF graph is not needed because the panel is a child of dsi. Remove
the ports node in DSI node.

Signed-off-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Andi Shyti <andi.shyti@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>