arm64: PCI: Drop DT IRQ allocation from pcibios_alloc_irq()

With the introduction of struct pci_host_bridge.map_irq pointer it is
possible to assign IRQs for all devices originating from a PCI host bridge
at probe time; this is implemented through pci_assign_irq() that relies on
the struct pci_host_bridge.map_irq pointer to map IRQ for a given device.

The benefits this brings are twofold:

- the IRQ for a device is assigned once at probe time
- the IRQ assignment works also for hotplugged devices

With all DT based PCI host bridges converted to the struct
pci_host_bridge.{map/swizzle}_irq hooks mechanism the DT IRQ allocation in
ARM64 pcibios_alloc_irq() is now redundant and can be removed.

Signed-off-by: Lorenzo Pieralisi <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Acked-by: Will Deacon <[e-mail]>

arch/arm64/kernel/pci.c

···
 	return res->start;
 }
 
+#ifdef CONFIG_ACPI
 /*
  * Try to assign the IRQ number when probing a new device
  */
 int pcibios_alloc_irq(struct pci_dev *dev)
 {
-	if (acpi_disabled)
-		dev->irq = of_irq_parse_and_map_pci(dev, 0, 0);
-#ifdef CONFIG_ACPI
-	else
-		return acpi_pci_irq_enable(dev);
-#endif
+	if (!acpi_disabled)
+		acpi_pci_irq_enable(dev);
 
 	return 0;
 }
+#endif
 
 /*
  * raw_pci_read/write - Platform-specific PCI config space access.