fs: Rename fs.h to fs_legacy.h

A new filesystem interface is coming, so rename the current header to
indicate that it is the old one.

Signed-off-by: Simon Glass <sjg@chromium.org>

cmd/fs.c

@@ -6,7 +6,7 @@
  */
 
 #include <command.h>
-#include <fs.h>
+#include <fs_legacy.h>
 
 static int do_size_wrapper(struct cmd_tbl *cmdtp, int flag, int argc,
 			   char *const argv[])