vfio: ccw: Merge BUSY and BOXED states

VFIO_CCW_STATE_BOXED and VFIO_CCW_STATE_BUSY have
identical actions for the same events.

Let's merge both into a single state to simplify the code.
We choose to keep VFIO_CCW_STATE_BUSY.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
Message-Id: <1539767923-10539-2-git-send-email-pmorel@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>