microblaze: timer: Update header

Update dates in header and add Xilinx to it.
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/kernel/timer.c

 /*
- * Copyright (C) 2007-2009 Michal Simek <monstr@monstr.eu>
+ * Copyright (C) 2007-2013 Michal Simek <monstr@monstr.eu>
+ * Copyright (C) 2012-2013 Xilinx, Inc.
  * Copyright (C) 2007-2009 PetaLogix
  * Copyright (C) 2006 Atmark Techno, Inc.
  *