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
diff --git a/target/board/BoardConfigGsiCommon.mk b/target/board/BoardConfigGsiCommon.mk
index 86f5bf1..237cd28 100644
--- a/target/board/BoardConfigGsiCommon.mk
+++ b/target/board/BoardConfigGsiCommon.mk
@@ -23,3 +23,6 @@
 # Pi GSI supports system-as-root
 TARGET_NO_RECOVERY := true
 BOARD_BUILD_SYSTEM_ROOT_IMAGE := true
+
+# Audio: must using XML format for Treblized devices
+USE_XML_AUDIO_POLICY_CONF := 1