Keep a copy of the space-separated PRODUCT_AAPT_CONFIG

That can be used to select dpi-specific prebuilt apks.

Change-Id: Ic68be8fc6fdb46f3ff8de490a35a042a31f1cb19
diff --git a/core/product_config.mk b/core/product_config.mk
index e4b68cf..e381dbe 100644
--- a/core/product_config.mk
+++ b/core/product_config.mk
@@ -306,8 +306,10 @@
 # Everyone gets nodpi assets which are density-independent.
 PRODUCT_AAPT_CONFIG += nodpi
 
+# Keep a copy of the space-separated config
+PRODUCT_AAPT_CONFIG_SP := $(PRODUCT_AAPT_CONFIG)
+
 # Convert spaces to commas.
-comma := ,
 PRODUCT_AAPT_CONFIG := \
     $(subst $(space),$(comma),$(strip $(PRODUCT_AAPT_CONFIG)))
 PRODUCT_AAPT_PREF_CONFIG := \