Effect factory: Load config from /odm, /vendor or /system

The effect framework only supports loading its config from /vendor/etc/.

As the audioeffects.conf supported to be loaded from /system and we want
to ease transition to xml,
As the audio policy config and the effect HW modules are can be loaded
from {"/odm/etc", "/vendor/etc", "/system/etc"},

Search for the audio effects xml config in /odm, then /vendor then
/vendor.

Bug: 38184704
Change-Id: I92a4e182fd16659eee2cf6481f8c2a646bf4f427
Test: media.audio_flinger dumpsys with config in /vendor and /system
      are identical
Signed-off-by: Kevin Rocard <krocard@google.com>