Make mainline device enable property split

This setting moves the PRODUCT_PROPERTY_OVERRIDES to
the vendor partition.

Bug: 80410283
Test: tail system/build.prop | grep ro.carrier=
      (empty)

Change-Id: I30d564fbd2dd3b56763ccff77979b223857f1c2f
diff --git a/target/board/BoardConfigMainlineCommon.mk b/target/board/BoardConfigMainlineCommon.mk
index ed69357..fc55408 100644
--- a/target/board/BoardConfigMainlineCommon.mk
+++ b/target/board/BoardConfigMainlineCommon.mk
@@ -46,3 +46,6 @@
 # Enable A/B update
 AB_OTA_UPDATER := true
 AB_OTA_PARTITIONS := system
+
+# Enable system property split for Treble
+BOARD_PROPERTY_OVERRIDES_SPLIT_ENABLED := true