sparc64: fatal trap should stop all cpus

"echo c > /proc/sysrq-trigger" does not result in a system crash. There
are two problems. One is that the trap handler ignores the global
variable, panic_on_oops. The other is that smp_send_stop() is a no-op
which leaves the other cpus running normally when one cpu panics.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>