Add ro.audio.ihaladaptervendorextension_enabled property

This property is used by libaudiohal@aidl to detect whether
the system_ext partition provides an instance of
IHalAdapterVendorExtension. This is a "system internal"
property because it belongs to `system_ext`.

Bug: 323989070
Test: atest audiorouting_test
Ignore-AOSP-First: coupled with Pixel change, will upstream
Change-Id: I81267da070958a70f2f3c4882718cac4600e3476
diff --git a/private/audioserver.te b/private/audioserver.te
index 7a5e8bc..74d5e88 100644
--- a/private/audioserver.te
+++ b/private/audioserver.te
@@ -105,3 +105,4 @@
 
 # Allow reading audio config props, e.g. af.fast_track_multiplier
 get_prop(audioserver, audio_config_prop)
+get_prop(audioserver, system_audio_config_prop)