Normally buildman wil try to configure U-Boot for a particular board on the
first commit that it builds in a series. Subsequent commits are built
without reconfiguring which normally works. Where it doesn't, buildman
automatically reconfigures and retries.

To fully emulate the way MAKEALL works, we should have an option to disable
this optimisation.

Add a -C option to cause buildman to always reconfigure on each commit.

Signed-off-by: Simon Glass <sjg@chromium.org>