Add SMM variable support for universal UEFI payload. By default they are disabled. Signed-off-by: Guo Dong <guo.dong@intel.com> Cc: Ray Ni <ray.ni@intel.com> Cc: Maurice Ma <maurice.ma@intel.com> Cc: Benjamin You <benjamin.you@intel.com> Reviewed-by: Ray Ni <ray.ni@intel.com> Reviewed-by: Benjamin You <benjamin.you@intel.com>