tty: serial: serial_txx9: remove struct uart_txx9_port

It's only a wrapper to struct uart_port, so unwrap the whole code.

No change in functionality is intended.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220307054348.31748-1-jslaby@suse.czSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>