sh: oops_enter()/oops_exit() in die().

As Russell helpfully pointed out on linux-arch:

	http://marc.info/?l=linux-arch&m=118208089204630&w=2

We were missing the oops_enter/exit() in the sh die() implementation.
As we do support lockdep, it's beneficial to add these calls so lockdep
properly disables itself in the die() case.

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