powerpc/xics: Add debug logging to the set_irq_affinity handlers

It really helps to know how the HW is configured when tweaking the IRQ
subsystem.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210701132750.1475580-20-clg@kaod.org