rc_input: add RC_PORT_CONFIG param to configure RC port

The parameter will only be available if the board defines an 'RC' serial
port in SERIAL_PORTS (in default.cmake).

Tools/serial/serial_params.c.jinja

@@ -52,6 +52,8 @@ PARAM_DEFINE_INT32(SER_{{ serial_device.tag }}_BAUD, {{ serial_device.default_ba
  *
  * Configure on which serial port to run {{ command.label }}.
  *
+ * {{ command.description_extended | replace("\n", " ") }}
+ *
  * @value 0 Disabled
 {% for serial_device in serial_devices -%}
  * @value {{ serial_device.index }} {{ serial_device.label }}