core: Add infrastructure for synchronizing HW and SW volume changes

core: Add infrastructure for synchronizing HW and SW volume changes

To make concurrent use of SW and HW volume glitchles their application
needs to be synchronized. For accurate synchronization the HW volume
needs to be applied in IO thread. This patch adds infrastructure to
delay the applying of HW volume to match with SW volume timing. To
avoid synchronization problems this patch moves many of the volume and
mute related functions from main thread to IO thread. All these
changes become active only if the sync volume flag for a sink has been
set. So, for this patch to have any effect it needs to be taken into
use by sink implementor.

Signed-off-by: Jyri Sarha <jyri.sarha@nokia.com>
Reviewed-by: Tanu Kaskinen <tanu.kaskinen@digia.com>
Reviewd-by: Colin Guthrie <cguthrie@mandriva.org>