patman: Update errors and warnings to use stderr

When warnings and errors are produced by tools they should be written to
stderr. Update the tout implementation to handle this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

tools/patman/tout.py

@@ -83,7 +83,10 @@ def _Output(level, msg, color=None):
         ClearProgress()
         if color:
             msg = _color.Color(color, msg)
-        print(msg)
+        if level < NOTICE:
+            print(msg, file=sys.stderr)
+        else:
+            print(msg)
 
 def DoOutput(level, msg):
     """Output a message to the terminal.