irqchip/loongson-pch-msi: Switch to MSI parent domains

Remove the global PCI/MSI irqdomain implementation and provide the
required MSI parent functionality by filling in msi_parent_ops, so the
PCI/MSI code can detect the new parent and setup per-device MSI domains.

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240815112608.26925-2-zhangtianyang@loongson.cn