genirq: Hide irq_cpu_{on,off}line() behind a deprecated option

irq_cpu_{on,off}line() are now only used by the Octeon platform.
Make their use conditional on this plaform being enabled, and
otherwise hidden away.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20211021170414.3341522-4-maz@kernel.org