Fix JFFS2 support for legacy NAND driver.

Some more NAND cleanup and small fixes.
diff --git a/drivers/nand/nand.c b/drivers/nand/nand.c
index dd80026..e1781fc 100644
--- a/drivers/nand/nand.c
+++ b/drivers/nand/nand.c
@@ -23,11 +23,7 @@
 
 #include <common.h>
 
-#ifdef CFG_NAND_LEGACY
-#error CFG_NAND_LEGACY defined in a file not using the legacy NAND support!
-#endif
-
-#if (CONFIG_COMMANDS & CFG_CMD_NAND)
+#if (CONFIG_COMMANDS & CFG_CMD_NAND) && !defined(CFG_NAND_LEGACY)
 
 #include <nand.h>