fs_mgr: use ro.persistent_properties.ready

Replace more complicated logic that determines that persistent
properties are now valid with a simple check of
ro.persistent_properties.ready.

Test: manual
Bug: 109821005
Change-Id: I8c63beb294377ea9ce6eb6336b83f529deedd830

private/adbd.te

@@ -78,6 +78,12 @@ get_prop(adbd, device_logging_prop)
 # Read device's serial number from system properties
 get_prop(adbd, serialno_prop)
 
+# Read device's overlayfs related properties and files
+userdebug_or_eng(`
+  get_prop(adbd, persistent_properties_ready_prop)
+  r_dir_file(adbd, sysfs_dt_firmware_android)
+')
+
 # Run /system/bin/bu
 allow adbd system_file:file rx_file_perms;