TTY: 68328serial, remove serial_state and friends

serial_state in 68328serial.h is a duplicated structure. One is
defined in linux/serial.h. So let us use that instead. And since the
serial flags are identical, use ones from there too.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Cc: linux-m68k@lists.linux-m68k.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>