audio policy: fix legacy Ad2P with advanced codecs

The changes for hybrid A2DP broke advanced codec support for devices
running a HAL V4.0 and no A2DP offload.

Fix: consider that if no encoded format is explicitely listed in the
device descriptor in audio policy configuration file, then no rule on
encoded format should be enforced.

Bug: 123399421
Test: connect Sony MDR-1 headphones and play music.
Change-Id: Idd13cf0e0cdeb71554b23d178e61cc1d82abea60