sh: Wire up oops reporting in the die notifier chain.

Commit 3f5a54e3

 ("ftrace: dump out ftrace
buffers to console on panic") added an ftrace buffer dumper that hooks
in to the die notifier chain and dumps out data in the oops path.

Unfortunately SH supported ftrace but didn't support DIE_OOPS, so add
that in and get it building again.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>