buildman: Move full-help processing to main

This does not need any of the control features. Move it out of main to
reduce the size of the do_buildman() function.

For Python 3.6 the -H feature will not work, but this does not seem to be
a huge problem, as it dates from 2016.

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