localmodconfig: Use Kbuild files too

In kbuild it is allowed to define objects in files named "Makefile"
and "Kbuild".
Currently localmodconfig reads objects only from "Makefile"s and misses
modules like nouveau.

Link: http://lkml.kernel.org/r/1437948415-16290-1-git-send-email-richard@nod.at

Cc: stable@vger.kernel.org
Reported-and-tested-by: Leonidas Spyropoulos <artafinde@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>