APCI: irq: Add support for multiple GSI domains

In an unfortunate departure from the ACPI spec, the LoongArch
architecture split its GSI space across multiple interrupt
controllers.

In order to be able to reuse the core code and prevent
architectures from reinventing an already square wheel, offer
the arch code the ability to register a dispatcher function
that will return the domain fwnode for a given GSI.

The ARM GIC drivers are updated to support this (with a single
domain, as intended).

Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Hanjun Guo <guohanjun@huawei.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Jianmin Lv <lvjianmin@loongson.cn>
Tested-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Link: https://lore.kernel.org/r/1658314292-35346-3-git-send-email-lvjianmin@loongson.cn