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