MIPS: Octeon: Use arch_setup_msi_irq()

The core code provides the same loop code except for the MSI-X reject. Move
that to arch_setup_msi_irq() and remove the duplicated code.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Link: https://lore.kernel.org/r/20211206210224.319201379@linutronix.de