pci, x86/io-apic: Allow PCI_IOAPIC to be user configurable on x86

pci, x86/io-apic: Allow PCI_IOAPIC to be user configurable on x86

This adjusts PCI_IOAPIC to be user configurable (possibly as a
module) on x86, since the base architecture code for adding
IO-APICs dynamically isn't there yet (and hence having the code
present everywhere is pretty pointless).

To make this consistent, a MODULE_DEVICE_TABLE() declaration
gets added, the class specifications get corrected (by properly
using PCI_DEVICE_CLASS() intended for purposes like this), and
the probe and remove functions get their sections adjusted.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Link: http://lkml.kernel.org/r/4EDDD71A02000078000659F1@nat28.tlf.novell.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>