Revert "patman: invoke the checkpatch.pl script with '--u-boot' and '--strict'"

This reverts commit 648d8186, because
it broke usage of patman on Linux, whose check script doesn't know
about '--strict' or '--u-boot'.

Reported-by: Sjoerd Simons <sjoerd@collabora.com>
Signed-off-by: Maxim Cournoyer <maxim.cournoyer@savoirfairelinux.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Sjoerd Simons <sjoerd@collabora.com>