patman: Add a Series-patchwork-url option

Add a commit tag to allow the Patchwork URL to be specified in a commit.
This can be handy for when you submit code to multiple projects but don't
want to use the -p option.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/series.py b/tools/patman/series.py
index 4457719..1d92bdb 100644
--- a/tools/patman/series.py
+++ b/tools/patman/series.py
@@ -16,7 +16,7 @@
 
 # Series-xxx tags that we understand
 valid_series = ['to', 'cc', 'version', 'changes', 'prefix', 'notes', 'name',
-                'cover_cc', 'process_log', 'links']
+                'cover_cc', 'process_log', 'links', 'patchwork_url']
 
 class Series(dict):
     """Holds information about a patch series, including all tags.