csky: Move $(core-y) into arch/csky/Kbuild

Use the standard obj-y form to specify the sub-directories under
arch/csky/. Only leave core-y += arch/csky/$(CSKYABI)/ there.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Guo Ren <guoren@kernel.org>

arch/csky/Kbuild

 # SPDX-License-Identifier: GPL-2.0-only
 
+obj-y += kernel/ mm/
+
 # for cleaning
 subdir- += boot

arch/csky/Makefile

@@ -61,8 +61,6 @@ KBUILD_AFLAGS += $(KBUILD_CFLAGS)
 
 head-y := arch/csky/kernel/head.o
 
-core-y += arch/csky/kernel/
-core-y += arch/csky/mm/
 core-y += arch/csky/$(CSKYABI)/
 
 libs-y += arch/csky/lib/ \