Blackfin: convert old boards to use COBJS-y Makefile style

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/board/bf537-stamp/Makefile b/board/bf537-stamp/Makefile
index e5ef9af..cb38b96 100644
--- a/board/bf537-stamp/Makefile
+++ b/board/bf537-stamp/Makefile
@@ -29,11 +29,13 @@
 
 LIB	= $(obj)lib$(BOARD).a
 
-COBJS	:= $(BOARD).o post-memory.o spi_flash.o cmd_bf537led.o nand.o
+COBJS-y	:= $(BOARD).o post-memory.o cmd_bf537led.o
+COBJS-$(CONFIG_CMD_EEPROM) += spi_flash.o
+COBJS-$(CONFIG_CMD_NAND)   += nand.o
 
-SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c)
-OBJS	:= $(addprefix $(obj),$(COBJS))
-SOBJS	:= $(addprefix $(obj),$(SOBJS))
+SRCS	:= $(SOBJS-y:.o=.S) $(COBJS-y:.o=.c)
+OBJS	:= $(addprefix $(obj),$(COBJS-y))
+SOBJS	:= $(addprefix $(obj),$(SOBJS-y))
 
 $(LIB):	$(obj).depend $(OBJS) $(SOBJS) $(obj)u-boot.lds
 	$(AR) $(ARFLAGS) $@ $(OBJS) $(SOBJS)