powerpc/pseries/pci: Add a domain_free_irqs() handler

The RTAS firmware can not disable one MSI at a time. It's all or
nothing. We need a custom free IRQ handler for that.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210701132750.1475580-9-clg@kaod.org