patman: Add a 'keep_change_id' setting

A Change-Id can be useful for traceability purposes, and some projects
may wish to have them preserved.  This change makes it configurable
via a new 'keep_change_id' setting.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
5 files changed