irqdomain: Fix domain registration race

Hierarchical domains created using irq_domain_create_hierarchy() are
currently added to the domain list before having been fully initialised.

This specifically means that a racing allocation request might fail to
allocate irq data for the inner domains of a hierarchy in case the
parent domain pointer has not yet been set up.

Note that this is not really any issue for irqchip drivers that are
registered early (e.g. via IRQCHIP_DECLARE() or IRQCHIP_ACPI_DECLARE())
but could potentially cause trouble with drivers that are registered
later (e.g. modular drivers using IRQCHIP_PLATFORM_DRIVER_BEGIN(),
gpiochip drivers, etc.).

Fixes: afb7da83b9f4 ("irqdomain: Introduce helper function irq_domain_add_hierarchy()")
Cc: [email protected]      # 3.19
Signed-off-by: Marc Zyngier <[email protected]>
[ johan: add commit message ]
Signed-off-by: Johan Hovold <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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