sh: convert makefiles to Kbuild style

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
diff --git a/arch/sh/cpu/sh4/Makefile b/arch/sh/cpu/sh4/Makefile
index 5680d61..38c6188 100644
--- a/arch/sh/cpu/sh4/Makefile
+++ b/arch/sh/cpu/sh4/Makefile
@@ -8,27 +8,5 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-LIB	= $(obj)lib$(CPU).o
-
-START	= start.o
-COBJS	= cpu.o interrupts.o watchdog.o cache.o
-
-SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c)
-OBJS	:= $(addprefix $(obj),$(COBJS))
-SOBJS	:= $(addprefix $(obj),$(SOBJS))
-
-all:    $(START) $(LIB)
-
-$(LIB):	$(OBJS) $(SOBJS)
-	$(call cmd_link_o_target, $(OBJS) $(SOBJS))
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################
+extra-y	= start.o
+obj-y	= cpu.o interrupts.o watchdog.o cache.o