get_maintainer.pl: tighten up git contributors cc list

get_maintainer in U-Boot is configured to include contributors and patch
reviewers from the git history in the CC list, going back 1 year if they
have contributed more than 5% of the patches.

This is well suited to some core U-Boot code that has a long history and
doesn't get much love from any dedicated maintainer but for newer code
and board code in general as well as defconfigs it can be frustrating
for some contributors who do not wish to be CC'd on patches as well as a
general issue when dead emails are included.

While it would be desirable to just remove the --git flag and encourage
those interested to configure lei or just add themselves to MAINTAINERS
it perhaps makes more sense to phase it out gradually.

As a first step, reduce the time period that will be checked in the git
history from 1 year to 6 months, this still offers plenty of leeway for
contributions to the last 1/2 U-Boot releases. In addition, bump up the
required percentage of contributions from 5% to 15% and reduce the limit
on the number of "git maintainers" (i.e. unique S-o-b/A-b/R-b tags) from
5 to 2.

These changes should reduce the size of CC lists while still including
recent active contributors.

Signed-off-by: Casey Connolly <casey.connolly@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

.get_maintainer.conf

@@ -1 +1,6 @@
---find-maintainer-files --git --maintainer-path=.
+--find-maintainer-files
+--git
+--git-min-percent 15
+--git-since 6-months-ago
+--git-max-maintainers 2
+--maintainer-path=.