make ro.persistent_properties.ready accessible for hidl client

 - compared to ro.boottime, this one does not pass time info

bug: 35178781
bug: 34274385
Test: reboot

Change-Id: I6a7bf636a3f201653e2890751d5fa210274c9ede
diff --git a/private/property_contexts b/private/property_contexts
index 7845505..c205e59 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -84,6 +84,8 @@
 # set at runtime by system_server.
 ro.build.fingerprint    u:object_r:fingerprint_prop:s0
 
+ro.persistent_properties.ready  u:object_r:persistent_properties_ready_prop:s0
+
 # ctl properties
 ctl.bootanim            u:object_r:ctl_bootanim_prop:s0
 ctl.dumpstate           u:object_r:ctl_dumpstate_prop:s0