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/delta/nand.c b/board/delta/nand.c
index b007b09..4ce78a1 100644
--- a/board/delta/nand.c
+++ b/board/delta/nand.c
@@ -23,7 +23,7 @@
 #include <common.h>
 
 #if defined(CONFIG_CMD_NAND)
-#if !defined(CFG_NAND_LEGACY)
+#if !defined(CONFIG_NAND_LEGACY)
 
 #include <nand.h>
 #include <asm/arch/pxa-regs.h>