pc: memhp: do not emit inserting event for coldplugged DIMMs

pc: memhp: do not emit inserting event for coldplugged DIMMs

currently acpi_memory_plug_cb() sets is_inserting for
cold- and hot-plugged DIMMs as result ASL MHPD.MSCN()
method issues device check even for every coldplugged
DIMM. There isn't much harm in it but if we try to
unplug such DIMM, OSPM will issue device check
intstead of device eject event. So OSPM won't eject
memory module as expected and it will try to eject it
only when another memory device is hot-(un)plugged.

As a fix do not set 'is_inserting' event and do not
issue SCI for cold-plugged DIMMs as they are
enumerated and activated by OSPM during guest's boot.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>