Effects factory: Implement xml config loading

For treble, files shared between vendor and system must have a schema.
As .conf did not support such feature, transition to an xml based
configuration file.

This new format has several changes:
 - library path are now relative to the standard effect directories
 - effect parameters are no longer supported (nobody used them)

Test: Check that the dumpsys is similar than with the legacy formal
Bug: 37492580
Change-Id: I01d79d016ec0bf52fbaf073f4452862214ab9344
Signed-off-by: Kevin Rocard <krocard@google.com>