Revert "Removing N from PLATFORM_VERSION_ALL_CODENAMES"

This reverts commit 5fcdec083edf0eb3cbc8cdf05626d1713df677f1.

Bug: 29194920
Bug: 28809789
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 5acd4dd..bdfc65a 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -75,7 +75,7 @@
   # This is all of the development codenames that are active.  Should be either
   # the same as PLATFORM_VERSION_CODENAME or a comma-separated list of additional
   # codenames after PLATFORM_VERSION_CODENAME.
-  PLATFORM_VERSION_ALL_CODENAMES := $(PLATFORM_VERSION_CODENAME)
+  PLATFORM_VERSION_ALL_CODENAMES := $(PLATFORM_VERSION_CODENAME),N
 endif
 
 ifeq "REL" "$(PLATFORM_VERSION_CODENAME)"