dt-bindings: display: rockchip: rockchip,dw-hdmi: remove port property

The hdmi-connector nodes are now functional and the new way to model
hdmi ports nodes with both in and output port subnodes. Unfortunately
with the conversion to YAML the old method with only an input port node
was used. Later the new method was also added to the binding.
A binding must be unambiguously, so remove the old port property
entirely and make port@0 and port@1 a requirement as all
upstream dts files are updated as well and because checking
deprecated stuff is a bit pointless.
Update the example to avoid use of the removed property.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/a493c65e-7cf9-455f-95d5-8c98cad35710@gmail.com