Kinetis:USB-FS driver

   Removed the notion of attached. The khci_usbattach is call early in
   the init either in board_initalize or in board_app_initalize. In
   either case it is always done prior to the the class register.
   Therefore the khci_usbattach call only set a flag, and that
   flag is only tested in the class register. The class register will
   enable the soft connect pull up.