m68knommu: add info about removing mcfserial

Schedule a removal for this driver. Alternative driver is available for
a while now.

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