Add USE_XML_AUDIO_POLICY_CONF to GSI

USE_XML_AUDIO_POLICY_CONF is must for Treble device, so it is
also must on GSI. The settings is missed when creating GSI
aosp_$arch, add it back by this patch.

Bug: 110988359
Bug: 111053290
Test: build aosp_arm64 and build pass
Change-Id: I95f096e58350233fdcc8de115cc1691360070445