PCI: Build setup-irq.o for arm64

ARM64 requires setup-irq.o to provide pci_fixup_irqs() implementation.  We
are adding this now to support the pci-host-generic host controller, but we
enable it for ARM64 PCI so that other host controllers can use this as
well.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>