patman: Import 'configparser' lower case to be python 3.x safe

In python 3.x module names used in import statements are case sensitive,
and the configparser module is named in all lower-case. Import it as such
in order to avoid errors when running with python 3.x.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Acked-by: Simon Glass <sjg@chromium.org>