ACPI: Add _OST support for ACPI container hotplug

Changed container_notify_cb() to call ACPI _OST method when ACPI
container hotplug operation has completed. Slightly restructured
the code with the same logic. The function sets eject_pending bit
for an eject request since it does not initiate hot-remove operation.
This bit is checked by the sysfs eject handler to determine if the
request is originated from an ACPI eject notification.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>