Add mmd.enabled_aconfig to sepolicy

"mmd --set-property" command copies AConfig flag to
"mmd.enabled_aconfig" system property to control mmd whether to start
or not at aosp/3368262.

Bug: 375431994
Test: manual

Change-Id: I27691243d9eed73fff9baccd9d23a346c18d7f4c
diff --git a/private/mmd.te b/private/mmd.te
index 193c307..4e49519 100644
--- a/private/mmd.te
+++ b/private/mmd.te
@@ -5,6 +5,9 @@
 
 init_daemon_domain(mmd)
 
+# Set mmd.enabled_aconfig properties.
+set_prop(mmd, mmd_prop)
+
 # mmd binder setup
 add_service(mmd, mmd_service)
 binder_use(mmd)