staging: comedi: new driver usbduxsigma

This adds a new driver file usbduxsigma which is the driver for
a new board by ITL. The driver has been tested and is working fine.

Signed-off-by: Bernd Porr <berndporr@f2s.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>