crossystem: support standard --help flag

BUG=chromium:765499
TEST=unittests pass
BRANCH=None

Change-Id: I5c5118c44897d89e5116a9fce49bacbf16704dd8
Reviewed-on: https://chromium-review.googlesource.com/668658
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
1 file changed