patman: Add Series-process-log tag to sort/uniq change logs

For some series with lots of changes it is annoying that duplicate change
log items are not caught. It is also helpful sometimes to sort the change
logs.

Add a Series-process-log tag to enable this, which can be placed in a
commit to control this.

The change to the Cc: line is to fix a checkpatch warning.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>