Configure audio effects libraries with relative path

audio effects.conf legacy format had the libraries specified
in absolute path.
Nevertheless those libraries must be in specific folders.
The .conf loader used to strip the prefix of the paths then
try to load the libraries in those specific folders.

With new xml format the user only has to specify the name of the library
and the loader will load it from the known folders.

Test: run xmllint against a config with absolute paths
Bug: 37492580
Change-Id: I2863e04b3cdf0c6758d9f7be33796621fee527ed
Signed-off-by: Kevin Rocard <krocard@google.com>