Add PRODUCT_SYSTEM_DEFAULT_PROPERTIES

PRODUCT_SYSTEM_DEFAULT_PROPERTIES will be used to define system default
properties which should be installed in system partition.

Bug: 64661857
Test: confirmed that ART default properties are stored in
/system/etc/prop.default when they were defined in
PRODUCT_SYSTEM_DEFAULT_PROPERTIES.

Change-Id: Ia08c25d0c5805381c6e3fe63dd1d171e8d195b90
diff --git a/core/Makefile b/core/Makefile
index 7fed968..4cbf8a9 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -110,7 +110,8 @@
 endif
 ALL_DEFAULT_INSTALLED_MODULES += $(INSTALLED_DEFAULT_PROP_TARGET)
 FINAL_DEFAULT_PROPERTIES := \
-    $(call collapse-pairs, $(ADDITIONAL_DEFAULT_PROPERTIES))
+    $(call collapse-pairs, $(ADDITIONAL_DEFAULT_PROPERTIES)) \
+    $(call collapse-pairs, $(PRODUCT_SYSTEM_DEFAULT_PROPERTIES))
 ifndef property_overrides_split_enabled
   FINAL_DEFAULT_PROPERTIES += \
       $(call collapse-pairs, $(PRODUCT_DEFAULT_PROPERTY_OVERRIDES))