Well, as far as I can see from Linux kernel source this "add port"-functionality is a special feature of the serial core within the linux kernel. If you want to have similar behaviour for a custom driver which does not interact with the serial core then you would have to implement this by yourself.
The uart_add_one_port() function is used by platform specific UART drivers like  in order to register the different UART's available on the platform. Each UART is represented by an own set of hardware registers and this function publishes these information to the kernel (serial core).
You could also have a look at the linux kernel documentation in .
Hope this helps a bit.