efivars: make new_var and del_var binary sysfs files

These files should not be "normal" sysfs files as they really are binary
ones.  This patch makes them binary files and saves code in doing so.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Tested-by: Matt Domsch <Matt_Domsch@dell.com>
Cc: Matt Tolentino <matthew.e.tolentino@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>