nds32: Convert Makefiles to use COBJS-y style

Signed-off-by: Kuan-Yu Kuo <ken.kuoky@gmail.com>
Cc: Macpaul Lin <macpaul@gmail.com>
diff --git a/arch/nds32/lib/Makefile b/arch/nds32/lib/Makefile
index 705e1ff..022b21a 100644
--- a/arch/nds32/lib/Makefile
+++ b/arch/nds32/lib/Makefile
@@ -29,12 +29,15 @@
 
 LIB	= $(obj)lib$(ARCH).o
 
-OBJS	:= board.o cache.o interrupts.o
+COBJS-y += board.o
+COBJS-y += cache.o
 COBJS-$(CONFIG_CMD_BOOTM) += bootm.o
+COBJS-y += interrupts.o
 
-all:	$(LIB)
+SRCS  := $(SOBJS-y:.o=.S) $(COBJS-y:.o=.c)
+OBJS	:= $(addprefix $(obj),$(SOBJS-y) $(COBJS-y))
 
-$(LIB):	$(OBJS) $(SOBJS)
+$(LIB): $(obj).depend $(OBJS)
 	$(call cmd_link_o_target, $(OBJS))
 
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