arm64: dts: renesas: rz-smarc-du-adv7513: Simplify DU port configuration

arm64: dts: renesas: rz-smarc-du-adv7513: Simplify DU port configuration

The SoC dtsi already defines the du node with its ports hierarchy,
including the du_out_rgb endpoint node under port@0.  There is no need
to redefine the entire ports/port@0 structure in the board-level dtsi.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20260420132211.1350656-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>