This also meant implementing software volume support, and since this is the last backend to do so, make that interface pure virtual again. In some cases the test needed tweaks. Change-Id: Ie429863f187b43802cdd4f16d841929e0cb0e729 Reviewed-by: Kurt Korbatits <kurt.korbatits@nokia.com> Reviewed-by: Dmytro Poplavskiy <dmytro.poplavskiy@nokia.com>