m68knommu: m68knommu: add old stack trace method

The old method is used when frame pointers are not available.
Also fix formating with CONFIG_KALLSYMS=n which eliminates \n.

Signed-off-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>