patman: Respect include directive on Git config lookup

patman: Respect include directive on Git config lookup

People may put their user name and email in a local config file and
reference it by the include.* directives, however `git config --global`
doesn't look up the included configs by default.

Enable the --includes option explicitly to support such use cases.

Signed-off-by: Fei Shao <fshao@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>