staging: speakup: migrate acntsa, bns, dummy and txprt to ttyio

This changes the above five synths to TTY-based comms. They were chosen as a
first pass because their serial comms are straightforward, i.e. they don't use
serial input and don't do internal port knocking.

Signed-off-by: Okash Khawaja <okash.khawaja@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>