sh: move core-y in arch/sh/Makefile to arch/sh/Kbuild

Use obj-y to clean up Makefile.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

arch/sh/Kbuild

 # SPDX-License-Identifier: GPL-2.0-only
+obj-y				+= kernel/ mm/ boards/
+obj-$(CONFIG_SH_FPU_EMU)	+= math-emu/
+obj-$(CONFIG_USE_BUILTIN_DTB)	+= boot/dts/

arch/sh/Makefile

@@ -116,11 +116,6 @@ export ld-bfd
 
 head-y	:= arch/sh/kernel/head_32.o
 
-core-y				+= arch/sh/kernel/ arch/sh/mm/ arch/sh/boards/
-core-$(CONFIG_SH_FPU_EMU)	+= arch/sh/math-emu/
-
-core-$(CONFIG_USE_BUILTIN_DTB)	+= arch/sh/boot/dts/
-
 # Mach groups
 machdir-$(CONFIG_SOLUTION_ENGINE)		+= mach-se
 machdir-$(CONFIG_SH_HP6XX)			+= mach-hp6xx