genconfig.py: Print defconfig next to warnings

At present we sometimes see warnings of the form:

/tmp/tmpMA89kB:36: warning: overriding the value of CMD_SPL.
	Old value: "y", new value: "y".

This is not very useful as it does not show whch defconfig file it relates
to. Update the tool to show this.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/genboardscfg.py

@@ -124,7 +124,7 @@ class KconfigScanner:
         os.environ['srctree'] = os.getcwd()
         os.environ['UBOOTVERSION'] = 'dummy'
         os.environ['KCONFIG_OBJDIR'] = ''
-        self._conf = kconfiglib.Config()
+        self._conf = kconfiglib.Config(print_warnings=False)
 
     def __del__(self):
         """Delete a leftover temporary file before exit.
@@ -166,7 +166,10 @@ class KconfigScanner:
                 else:
                     f.write(line[colon + 1:])
 
-        self._conf.load_config(self._tmpfile)
+        warnings = self._conf.load_config(self._tmpfile)
+        if warnings:
+            for warning in warnings:
+                print '%s: %s' % (defconfig, warning)
 
         try_remove(self._tmpfile)
         self._tmpfile = None