PCI: mediatek-gen3: Switch to msi_create_parent_irq_domain()

Switch to msi_create_parent_irq_domain() from pci_msi_create_irq_domain()
which was using legacy MSI domain setup.

Signed-off-by: Nam Cao <namcao@linutronix.de>
[mani: reworded commit message & fixed merge conflict]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
[bhelgaas: rebase on dev_fwnode() conversion]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/bfbd2e375269071b69e1aa85e629ee4b7c99518f.1750858083.git.namcao@linutronix.de