Add Volume per Attributes setter/getters

This patch adds in AudioSystem setter/getter of volume index
and also getter on index min and max according to the given
audio attributes.

Bug: 124767636
Test: dumpsys media.audio_policy
Change-Id: Ia20fcfbf5e20c98de5eb07551c299dc99d678fb8
Signed-off-by: François Gaffie <francois.gaffie@renault.com>