cros_bundle_firmware: Add messages for GBB command line overrides

When overriding GBB flags on the command line, print a helpful message
so the user knows what is going on.

BUG=chromium-os:33312
TEST=manual
Run cros_bundle_firmware with '--gbb-flags' arguments and see that the
messages appear.

Change-Id: I4f8c44df39f837615422eea1f93a521fb3eebc55
Reviewed-on: https://gerrit.chromium.org/gerrit/38403
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Reviewed-by: Che-Liang Chiou <clchiou@chromium.org>
Commit-Ready: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
diff --git a/host/lib/bundle_firmware.py b/host/lib/bundle_firmware.py
index 016cfe7..e36af70 100644
--- a/host/lib/bundle_firmware.py
+++ b/host/lib/bundle_firmware.py
@@ -371,13 +371,17 @@
           raise ValueError("Invalid GBB flag '%s'" % flag)
         if oper == '+':
           gbb_flags |= value
+          self._out.Notice("Cmdline: Enabling %s." % flag)
         elif oper == '-':
           gbb_flags &= ~value
+          self._out.Notice("Cmdline: Disabling %s." % flag)
         else:
           if use_base_value:
             gbb_flags = 0
             use_base_value = False
+            self._out.Notice('Cmdline: Resetting flags to 0')
           gbb_flags |= value
+          self._out.Notice("Cmdline: Enabling %s." % flag)
 
     return gbb_flags