[MTE] Allow system_app to write memtag property.

Bug: 206895651
Change-Id: I6463965c094b9b3c4f3f70929a09e109ee9c84b9
diff --git a/private/system_app.te b/private/system_app.te
index ce76b69..460ad4b 100644
--- a/private/system_app.te
+++ b/private/system_app.te
@@ -34,6 +34,7 @@
 allow system_app icon_file:file r_file_perms;
 
 # Write to properties
+set_prop(system_app, arm64_memtag_prop)
 set_prop(system_app, bluetooth_a2dp_offload_prop)
 set_prop(system_app, bluetooth_audio_hal_prop)
 set_prop(system_app, bluetooth_prop)