patman: Provide an option to run in single-threaded mode

Patman normally sends multiple concurrent requests to the patchwork
server, as this is faster. Provide an option to disable this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/cmdline.py b/tools/patman/cmdline.py
index a7327a2..cf32716 100644
--- a/tools/patman/cmdline.py
+++ b/tools/patman/cmdline.py
@@ -130,6 +130,8 @@
         help='Name of branch to create with collected responses')
     status.add_argument('-f', '--force', action='store_true',
                         help='Force overwriting an existing branch')
+    status.add_argument('-T', '--single-thread', action='store_true',
+                        help='Disable multithreading when reading patchwork')
 
     # Parse options twice: first to get the project and second to handle
     # defaults properly (which depends on project)