ACPI / hotplug / PCI: Rework the handling of eject requests

To avoid the need to install a hotplug notify handler for each ACPI
namespace node representing a device and having a matching scan
handler, move the check whether or not the ejection of the given
device is enabled through its scan handler from acpi_hotplug_notify_cb()
to acpi_generic_hotplug_event().  Also, move the execution of
ACPI_OST_SC_EJECT_IN_PROGRESS _OST to acpi_generic_hotplug_event(),
because in acpi_hotplug_notify_cb() or in acpi_eject_store() we really
don't know whether or not the eject is going to be in progress (for
example, acpi_hotplug_execute() may still fail without queuing up the
work item).

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