m68knommu: ColdFire add support for kernel preemption (missing chunk)

As the subject says this patch adds the support for kernel preemption on
m68knommu Coldfire.  I thing the same changes could be applied to 68360 &
68328 but since I don't have the HW, I don't touch it.  Kconfig enables the
preemption item only on coldfire.

This is a missing chunk from Sebastian's original patch that I lost from the
first submission.

Signed-off-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>