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>
diff --git a/tools/buildman/main.py b/tools/buildman/main.py
index d9ad836..9a1d599 100755
--- a/tools/buildman/main.py
+++ b/tools/buildman/main.py
@@ -6,6 +6,11 @@
 
 """See README for more information"""
 
+try:
+    from importlib.resources import files
+except ImportError:
+    # for Python 3.6
+    import importlib_resources
 import os
 import sys
 
@@ -19,6 +24,7 @@
 from buildman import cmdline
 from buildman import control
 from u_boot_pylib import test_util
+from u_boot_pylib import tools
 
 def run_tests(skip_net_tests, debug, verbose, args):
     """Run the buildman tests
@@ -64,6 +70,9 @@
         return run_tests(options.skip_net_tests, options.debug, options.verbose,
                          args)
 
+    elif options.full_help:
+        tools.print_full_help(str(files('buildman').joinpath('README.rst')))
+
     # Build selected commits for selected boards
     else:
         bsettings.Setup(options.config_file)