[SPARC]: dump_stack for sparc

Bob Breuer wrote a patch to add dump_stack for sparc. Supposedly, this
was applied, but it doesn't exist in 2.6.11.

This is the same patch, rediffed against 2.6.11.

Signed-off-by: Tom 'spot' Callaway <tcallawa@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>