The MIPS implementation of die() forgets to call notify_die() and thus notifiers
registered via register_die_notifier() are not called. This results in kgdb not
being activated on exceptions.
The only subtlety is that notify_die declares its regs argument w/o const, so
the const had to be removed from mips die() as well.
[Ralf: Fixed build error for SGI IP22 and IP28 platforms.]