ACPI / memhotplug: don't allow to eject the memory device if it is being used

We eject the memory device even if it is in use.  It is very dangerous,
and it will cause the kernel to be panicked.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>