buildman: Provide an argument to the -R option

Allow writing the file to a selected location, since otherwise this is
controlled by the buildman configuration, so cannot be determined by the
caller.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: https://source.denx.de/u-boot/u-boot/-/issues/17
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index fc9e926..89010ea 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -209,6 +209,8 @@
         if not os.path.exists(options.output_dir):
             os.makedirs(options.output_dir)
         board_file = os.path.join(options.output_dir, 'boards.cfg')
+        if options.regen_board_list and options.regen_board_list != '-':
+            board_file = options.regen_board_list
 
         brds = boards.Boards()
         if options.maintainer_check: