patman: Attach warnings to individual patches

At present warnings are produced across the whole set of patches when
parsing them. It is more useful to associate each warning with the patch
(or commit) that generated it.

Attach warnings to the Commit object and move them out of PatchStream.
Also avoid generating duplicate warnings for the same commit.

Signed-off-by: Simon Glass <sjg@chromium.org>
2 files changed