patman: Add a setting for the Patchwork URL

Add an argument to allow specifying the the patchwork URL. This also adds
this feature to the settings file, either globally, or on a per-project
basis.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/README b/tools/patman/README
index 49b7359..639c994 100644
--- a/tools/patman/README
+++ b/tools/patman/README
@@ -113,6 +113,7 @@
 process_tags: False
 verbose: True
 smtp_server: /path/to/sendmail
+patchwork_server: https://patchwork.ozlabs.org
 
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