buildman: Only print toolchain probing with -v

At present --list-tool-chains prints a lot of information about the
toolchain-probing process. This is generally not very interesting.
Update buildman to print this only if --list-tool-chains is given
with -v.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index 96f8ccf..c900211 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -164,7 +164,7 @@
 
     if no_toolchains:
         toolchains.GetSettings()
-        toolchains.Scan(options.list_tool_chains)
+        toolchains.Scan(options.list_tool_chains and options.verbose)
     if options.list_tool_chains:
         toolchains.List()
         print