Add a new API named acpi_send_gpe_event() to send hotplug SCI.
This API can be used by pci, cpu and memory hotplug.

This patch is rebased on master.
Signed-off-by: NZhu Guihua <zhugh.fnst@cn.fujitsu.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>