acpi, ich9: Add hotunplug request cb for ich9.

acpi, ich9: Add hotunplug request cb for ich9.

Memory and CPU hot unplug are both asynchronous procedures.
They both need unplug request cb when the unplug operation happens.

This patch adds hotunplug request cb for ich9, and memory and CPU
hot unplug will share it.

Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Signed-off-by: Zhu Guihua <zhugh.fnst@cn.fujitsu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>