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 <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/pci.c

@@ -39,20 +39,18 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 	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.