Update Config-Xeno submodule:  Add CONFIG_PREEMPT_NONE

From submodule commit log:

  Gilles's recommendation:
  http://permalink.gmane.org/gmane.linux.real-time.xenomai.users/18499

    No, as I said, in my experience, turning CONFIG_PREEMPT off,
    setting it to CONFIG_PREEMPT_NONE, results in shorter worst case
    latencies for Xenomai.

Fixes #2