buildman: Support in-tree builds

At present buildman always builds out-of-tree, that is it uses a separate
output directory from the source directory. Normally this is what you want,
but it is important that in-tree builds work also. Some Makefile changes may
break this.

Add a -i option to tell buildman to use in-tree builds, so that it is easy
to test this feature.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index a737fd1..2dd8043 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -158,6 +158,7 @@
         builder.force_build = options.force_build
         builder.force_build_failures = options.force_build_failures
         builder.force_reconfig = options.force_reconfig
+        builder.in_tree = options.in_tree
 
         # Work out which boards to build
         board_selected = boards.GetSelectedDict()