patman: Add new tags for finer-grained changelog control

patman: Add new tags for finer-grained changelog control

By default patman generates a combined changelog for the cover letter. This
may not always be desirable.

Many patches may have the same changes. These can be coalesced with
"Series-process-log: uniq", but this is imperfect. Similar changes like
"Move foo to patch 7" will not be merged with the similar "Move foo to this
patch from patch 6".

Changes may not make sense outside of the patch they are written for. For
example, a change line of "Add check for bar" does not make sense outside
of the context in which bar might be checked for. Some changes like "New"
or "Lint" may be repeated many times throughout different change logs, but
carry no useful information in a summary.

Lastly, I like to summarize the broad strokes of the changes I have made in
the cover letter, while documenting all the details in the appropriate
patches. I think this makes it easier to get a good feel for what has
changed, without making it difficult to wade through every change in the
whole series.

This patch adds two new tags to add changelog entries which only appear in
the cover letter, or only appear in the commit. Changes documented with
"Commit-changes" will only appear in the commit, and will not appear in the
cover letter. Changes documented with "Cover-changes" will not appear in
any commit, and will only appear in the cover letter.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>