Use Volume Group core callback in volume preference rather than intent

In order to prevent misalignement between hard-coded stream aliases,
this CL allows to use the Volume Group cb to update the SeekBarVolume.

The ultimate step would be to remove stream aliases from audioserver.

Bug: 124767636
Test: dumpsys media.audio_policy
Change-Id: Ide99e9dd97669e880d0d253102533c72070012a1
Signed-off-by: François Gaffie <francois.gaffie@renault.com>