LoongArch: Prepare to support multiple pch-pic and pch-msi irqdomain

For systems with two chipsets, there are two related pch-pic and
pch-msi irqdomains, each of which has the same node id as its
parent irqdomain. So we use a structure to mantain the relation
of node and it's parent irqdomain as pch irqdomin, the 'pci_segment'
field is only used to match the pci segment of a pci device when
setting msi irqdomain for the device.

struct acpi_vector_group {
        int node;
        int pci_segment;
        struct irq_domain *parent;
};

The field 'pci_segment' and 'node' are initialized from MCFG, and
the parent irqdomain driver will set field 'parent' by matching same
'node'.

Signed-off-by: Jianmin Lv <lvjianmin@loongson.cn>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/1658314292-35346-7-git-send-email-lvjianmin@loongson.cn