drivers/mtd/nand: Move conditional compilation to Makefile

rename CFG_NAND_LEGACY to CONFIG_NAND_LEGACY

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/board/netta/netta.c b/board/netta/netta.c
index 1183f33..bc31386 100644
--- a/board/netta/netta.c
+++ b/board/netta/netta.c
@@ -555,7 +555,7 @@
 	return 0;
 }
 
-#if defined(CONFIG_CMD_NAND) && defined(CFG_NAND_LEGACY)
+#if defined(CONFIG_CMD_NAND) && defined(CONFIG_NAND_LEGACY)
 
 #include <linux/mtd/nand_legacy.h>