Document the devicetree bindings for the CSI-2 inputs available on Gen3.
There is a need to add a custom property 'renesas,id' and to define
which CSI-2 input is described in which endpoint under the port@1 node.
This information is needed since there are a set of predefined routes
between each VIN and CSI-2 block. This routing table will be kept
inside the driver but in order for it to act on it it must know which
VIN and CSI-2 is which.