arm64: dts: rockchip: add label to first port of ISP on px30

arm64: dts: rockchip: add label to first port of ISP on px30

This will make it slightly easier for Device Trees (and Overlays) to
link the ISP controller to a video input such as a CSI camera while also
bringing it closer to what's been done already for the DSI controller.

Suggested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Link: https://lore.kernel.org/r/20250610-ringneck-haikou-video-demo-cam-v2-2-de1bf87e0732@cherry.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>