media: dt-bindings: nxp,imx8-isi: Refuse port@1 for single pipeline models

In case the hardware only supports just one pipeline, explicitly refuse
port@1 in ports node.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20240412095549.258870-1-alexander.stein@ew.tq-group.com
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>