staging/speakup: Add inflection synth parameter

The inflection parameter, i.e. the pitch range, allows to change the
expressiveness of the synthesized voice.  This is supported by the DEC
talk synths, and software synthesizers such as espeak/espeak-ng.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Link: https://lore.kernel.org/r/20200425193226.nv3zfd4k3xavi353@function


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>