drivers/mtd/onenand: Move conditional compilation to Makefile

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/drivers/mtd/onenand/Makefile b/drivers/mtd/onenand/Makefile
index 92074b2..1d35a57 100644
--- a/drivers/mtd/onenand/Makefile
+++ b/drivers/mtd/onenand/Makefile
@@ -25,8 +25,9 @@
 
 LIB	:= $(obj)libonenand.a
 
-COBJS	:= onenand_uboot.o onenand_base.o onenand_bbt.o
+COBJS-$(CONFIG_CMD_ONENAND)	:= onenand_uboot.o onenand_base.o onenand_bbt.o
 
+COBJS	:= $(COBJS-y)
 SRCS	:= $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(COBJS))