ACPI / PCI: Make PCI IRQ link driver use struct acpi_scan_handler

Make the ACPI PCI IRQ link driver use struct acpi_scan_handler
for representing the object used to set up ACPI interrupt links and
to remove data structures used for this purpose before unregistering
the corresponding ACPI device nodes.

This simplifies the code slightly and reduces the kernel's memory
footprint by avoiding the registration of a struct device_driver
object with the driver core and creation of its sysfs directory
which is unnecessary.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: Toshi Kani <toshi.kani@hp.com>