Move platform carrier config app name to string resource

This allows OEMs to customize the platform carrier config app.

Test: make
Change-Id: I1bc8f2b6e5d43c9686d14811c35bd3474a28595c
diff --git a/res/values/config.xml b/res/values/config.xml
index 1f23c6b..bd0ed10 100644
--- a/res/values/config.xml
+++ b/res/values/config.xml
@@ -218,4 +218,7 @@
 
     <!-- Whether the emergency only account can make emergency calls -->
     <bool name="config_pstnCanPlaceEmergencyCalls">true</bool>
+
+    <!-- The package name for the platform carrier config app, bundled with system image. -->
+    <string name="platform_carrier_config_package" translatable="false">com.android.carrierconfig</string>
 </resources>