ipmi/powernv: Convert to irq event interface

Convert the opal ipmi driver to use the new irq interface for events.

Signed-off-by: Alistair Popple <alistair@popple.id.au>
Acked-by: Corey Minyard <cminyard@mvista.com>
Cc: Corey Minyard <minyard@acm.org>
Cc: openipmi-developer@lists.sourceforge.net
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>