dt-bindings: smiapp: Align documentation with current practices

- The clock-lanes property is not needed for the sensors do not support
  lane reordering. (The information possibly present in existing clock-lane
  properties is simply not used.)

- There's no need to refer to the sensor device in the DT example, thus
  remove the label.

- Rename the "camera" device node as "camera-sensor".

- Rename the endpoint label as "smiapp_ep" (was: "smiapp_1_1"). There is
  in practice only one anyway.

- Remove the remote-endpoint documentation (it is covered by
  graph.txt to which video-interfaces.txt refers to).

- Add a note on the port and endpoint nodes.

These changes make the smiapp bindings a better example.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Rob Herring <robh@kernel.org>