genirq: Factor-in percpu irqaction creation

genirq: Factor-in percpu irqaction creation

Move the code creating a per-cpu irqaction into its own helper, so that
future changes to this code can be kept localised.

At the same time, fix the documentation which appears to say the wrong
thing when it comes to interrupts being automatically enabled
(percpu_devid interrupts never are).

Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Will Deacon <will@kernel.org>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20251020122944.3074811-14-maz@kernel.org