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 <[email protected]>
Acked-by: Jesse Barnes <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>