staging: speakup: Add pause command used on switching to graphical mode

For software speech syntheses to be able to manage concurrent audio card
access, they need to know when speakup stops emitting text to be spoken
because the console has switched to graphical mode.  This introduces a
PAUSE command to do so.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>