drivers/mtd/nand_legacy: Move conditional compilation to Makefile

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/drivers/mtd/nand_legacy/Makefile b/drivers/mtd/nand_legacy/Makefile
index 4e29c36..a1a9cc9 100644
--- a/drivers/mtd/nand_legacy/Makefile
+++ b/drivers/mtd/nand_legacy/Makefile
@@ -25,8 +25,11 @@
 
 LIB	:= $(obj)libnand_legacy.a
 
-COBJS	:= nand_legacy.o
+ifdef CONFIG_CMD_NAND
+COBJS-$(CONFIG_NAND_LEGACY)	:= nand_legacy.o
+endif
 
+COBJS	:= $(COBJS-y)
 SRCS	:= $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(COBJS))