audiopolicy: moves Stream Volume Curves to Engine

This CL moves the volume curves to the engine.
The configuration files of volume are now owned by the engine,
that is intended to become vendor specific.

Test: build, dumpsys media.audio_policy and checks the volume curves.
Bug: 124767636

Change-Id: I9e3b256d2eb89c8eac6b282db0e59ec3af47d76d
Signed-off-by: François Gaffie <francois.gaffie@renault.com>