m68knommu: add pretty back strace

With this patch and
 CONFIG_FRAME_POINTER=y
 CONFIG_KALLSYMS=y
The backtrace shows resolved function names and their numeric
address.

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