ACPI / hotplug / PCI: Unified notify handler for hotplug events

Using the hotplug context objects introduced previously rework the
ACPI-based PCI hotplug (ACPIPHP) core code so that all notifications
for ACPI device objects corresponding to the hotplug PCI devices are
handled by one function, handle_hotplug_event(), which recognizes
whether it has to handle a bridge or a function.

In addition to code size reduction it allows some ugly pieces of code
where notify handlers have to be uninstalled and installed again to
go away.  Moreover, it fixes a theoretically possible race between
handle_hotplug_event() and free_bridge() tearing down data structures
for the same handle.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>