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/property.te b/private/property.te
index e098fb2..e8d1eee 100644
--- a/private/property.te
+++ b/private/property.te
@@ -35,6 +35,7 @@
 system_internal_prop(localization_prop)
 system_internal_prop(logd_auditrate_prop)
 system_internal_prop(lower_kptr_restrict_prop)
+system_internal_prop(mmd_prop)
 system_internal_prop(net_464xlat_fromvendor_prop)
 system_internal_prop(net_connectivity_prop)
 system_internal_prop(netd_stable_secret_prop)