buildman: Add an option to show which boards caused which errors

Add a -l option to display a list of offending boards against each
error/warning line. The information will be shown in brackets as below:

02: wip
   sandbox: +   sandbox
       arm: +   seaboard
+(sandbox) arch/sandbox/cpu/cpu.c: In function 'timer_get_us':
+(sandbox) arch/sandbox/cpu/cpu.c:40:9: warning: unused variable 'i' [-Wunused-variable]
+(seaboard) board/nvidia/seaboard/seaboard.c: In function 'pin_mux_mmc':
+(seaboard) board/nvidia/seaboard/seaboard.c:36:9: warning: unused variable 'fred' [-Wunused-variable]
+(seaboard)      int fred;
+(seaboard)          ^

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index cb01158..06c9229 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -216,7 +216,8 @@
                                options)
 
         builder.SetDisplayOptions(options.show_errors, options.show_sizes,
-                                  options.show_detail, options.show_bloat)
+                                  options.show_detail, options.show_bloat,
+                                  options.list_error_boards)
         if options.summary:
             # We can't show function sizes without board details at present
             if options.show_bloat: