vendor: Add messaging app to power whitelist

* The messaging app is notorious for late notifications
  of messages. Whitelist it so it can be active during doze.

Change-Id: I932c89b27d76c114be67eaed62a3c021c219ca3a

config/permissions/lineage-power-whitelist.xml

@@ -16,4 +16,5 @@
 
 <config>
     <allow-in-power-save package="com.android.deskclock" />
+    <allow-in-power-save package="com.android.messaging" />
 </config>