PCI hotplug: move IOAPIC support from acpiphp to ioapic driver

This patch moves PCI I/O APIC support from acpiphp to a separate driver.

Like pciehp and shpchp, acpiphp handles PCI hotplug, i.e., addition and
removal of PCI adapters.  But in addition, acpiphp handles some ACPI
hotplug, such as the addition of new host bridges, and the I/O APIC
support was tangled up with that.

I don't think the I/O APIC support needs to be in acpiphp; PCI I/O APICs
usually appear as a function on a PCI host bridge, and we'll enumerate the
APIC before any of the devices behind the bridge that use it.

As far as I know, nobody actually uses I/O APIC hotplug.  It depends on
acpi_register_ioapic(), which is only implemented for ia64, and I don't
think any vendors have supported I/O chassis hotplug yet.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Reviewed-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
CC: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
CC: MUNEDA Takahiro <muneda.takahiro@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>