ACPI / memory-hotplug: call acpi_bus_trim() to remove memory device

The memory device has been ejected and powoffed, so we can call
acpi_bus_trim() to remove the memory device from acpi bus.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>