Convert CONFIG_BOOTFILE to Kconfig

This converts the following to Kconfig:
   CONFIG_BOOTFILE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/env_default.h b/include/env_default.h
index 21afd7f..7004a6f 100644
--- a/include/env_default.h
+++ b/include/env_default.h
@@ -77,7 +77,7 @@
 #ifdef	CONFIG_HOSTNAME
 	"hostname="	CONFIG_HOSTNAME	"\0"
 #endif
-#ifdef	CONFIG_BOOTFILE
+#ifdef CONFIG_USE_BOOTFILE
 	"bootfile="	CONFIG_BOOTFILE			"\0"
 #endif
 #ifdef	CONFIG_SYS_LOAD_ADDR