The change that removed the Master controls for Xonar D2(X) cards was
reverted, so we don't need to use the softvol plugin anymore ...
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Master Volume controls were removed from Xonar D2/D2X cards; add the
softvol plugin so that we have at least PCM volume.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>