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>
diff --git a/tools/patman/tout.py b/tools/patman/tout.py
index c7e3272..91a53f4 100644
--- a/tools/patman/tout.py
+++ b/tools/patman/tout.py
@@ -83,7 +83,10 @@
         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.