PCI, x86: Implement pcibios_alloc_irq() and pcibios_free_irq()

To support IOAPIC hotplug, we need to allocate PCI IRQ resources on demand
and free them when not used anymore.

Implement pcibios_alloc_irq() and pcibios_free_irq() to dynamically
allocate and free PCI IRQs.

Remove mp_should_keep_irq(), which is no longer used.

[bhelgaas: changelog]
Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
index 304eccb..d1aad69 100644
--- a/drivers/acpi/pci_irq.c
+++ b/drivers/acpi/pci_irq.c
@@ -484,14 +484,6 @@
 	if (!pin || !dev->irq_managed || dev->irq <= 0)
 		return;
 
-	/* Keep IOAPIC pin configuration when suspending */
-	if (dev->dev.power.is_prepared)
-		return;
-#ifdef	CONFIG_PM
-	if (dev->dev.power.runtime_status == RPM_SUSPENDING)
-		return;
-#endif
-
 	entry = acpi_pci_irq_lookup(dev, pin);
 	if (!entry)
 		return;
@@ -512,5 +504,6 @@
 	if (gsi >= 0) {
 		acpi_unregister_gsi(gsi);
 		dev->irq_managed = 0;
+		dev->irq = 0;
 	}
 }