PCI: xgene: Convert to MSI parent infrastructure

In an effort to move ARM64 away from the legacy MSI setup, convert the
XGENE PCIe driver to the MSI-parent infrastructure and let each device have
its own MSI domain.

[ tglx: Moved the struct out of the function call argument ]

Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250513172819.2216709-9-maz@kernel.org