PCI: Convert ioapic to be builtin only, not modular

Convert pci/ioapic.c to be builtin only, with no module option, so we can
support IO-APIC hotplug.  Also make it depend on X86_IO_APIC.

[bhelgaas: changelog]
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
diff --git a/drivers/pci/ioapic.c b/drivers/pci/ioapic.c
index 50ce680..2c2930e 100644
--- a/drivers/pci/ioapic.c
+++ b/drivers/pci/ioapic.c
@@ -113,6 +113,10 @@
 	.remove		= ioapic_remove,
 };
 
-module_pci_driver(ioapic_driver);
+static int __init ioapic_init(void)
+{
+	return pci_register_driver(&ioapic_driver);
+}
+module_init(ioapic_init);
 
 MODULE_LICENSE("GPL");