ACPI / hotplug: Carry out PCI root eject directly

Since _handle_hotplug_event_root() is run from the ACPI hotplug
workqueue, it doesn't need to queue up a work item to eject a PCI
host bridge on the same workqueue.  Instead, it can just carry out
the eject by calling acpi_bus_device_eject() directly, so make that
happen.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>