kbuild: Handle $(core-y) the same way as $(init-y), $(drivers-y) etc

$(CORE_FILES) did not quite follow the way the other vmlinux parts where
handled, due to potential init order dependencies. However, it seems
everybody is putting arch specific stuff in front, so we keep doing
this and nothing should break ;)

Makefile

@@ -252,17 +252,15 @@ drivers-y	:= drivers/ sound/
 networks-y	:= net/
 libs-y		:= lib/
 
-CORE_FILES	:= kernel/built-in.o mm/built-in.o fs/built-in.o \
-		   ipc/built-in.o security/built-in.o
-SUBDIRS		+= kernel mm fs ipc security
-
 include arch/$(ARCH)/Makefile
 
+core-y		+= kernel/ mm/ fs/ ipc/ security/
+
 SUBDIRS		+= $(patsubst %/,%,$(filter %/, $(init-y) $(init-m)))
 INIT		+= $(patsubst %/, %/built-in.o, $(init-y))
 
 SUBDIRS		+= $(patsubst %/,%,$(filter %/, $(core-y) $(core-m)))
-CORE_FILES	:= $(patsubst %/, %/built-in.o, $(core-y)) $(CORE_FILES)
+CORE_FILES	+= $(patsubst %/, %/built-in.o, $(core-y))
 
 SUBDIRS		+= $(patsubst %/,%,$(filter %/, $(drivers-y) $(drivers-m)))
 DRIVERS		+= $(patsubst %/, %/built-in.o, $(drivers-y))