MIPS: BMIPS: Remove use of irq_cpu_offline

irq_cpu_offline() is only used by MIPS and we should instead use
irq_migrate_all_off_this_cpu(). This will be helpful in order to remove
drivers/irqchip/irq-bcm7038-l1.c irq_cpu_offline callback which would
have got in the way of making this driver modular.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211020184859.2705451-2-f.fainelli@gmail.com