at91rm9200dk: Move conditional compilation to Makefile

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/board/atmel/at91rm9200dk/Makefile b/board/atmel/at91rm9200dk/Makefile
index 2d806d0..79d41d6 100644
--- a/board/atmel/at91rm9200dk/Makefile
+++ b/board/atmel/at91rm9200dk/Makefile
@@ -25,10 +25,16 @@
 
 LIB	= $(obj)lib$(BOARD).a
 
-COBJS	:= at91rm9200dk.o flash.o led.o mux.o partition.o
+COBJS-y += $(BOARD).o
+COBJS-y += flash.o
+COBJS-y += led.o
+ifdef CONFIG_HAS_DATAFLASH
+COBJS-$(CONFIG_DATAFLASH_MMC_SELECT) += mux.o
+COBJS-y += partition.o
+endif
 
-SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c)
-OBJS	:= $(addprefix $(obj),$(COBJS))
+SRCS	:= $(SOBJS:.o=.S) $(COBJS-y:.o=.c)
+OBJS	:= $(addprefix $(obj),$(COBJS-y))
 SOBJS	:= $(addprefix $(obj),$(SOBJS))
 
 $(LIB):	$(obj).depend $(OBJS) $(SOBJS)