s390x/pci: Unplug remaining requested devices on pcihost reset

s390x/pci: Unplug remaining requested devices on pcihost reset

When resetting the guest we should unplug and remove all devices that
are still pending.

With this patch, the requested device will be unplugged on reboot
(S390_RESET_EXTERNAL and S390_RESET_REIPL, which reset the pcihost bridge
via qemu_devices_reset()).

This approach is similar to what's done for acpi PCI hotplug in
acpi_pcihp_reset() -> acpi_pcihp_update() ->
acpi_pcihp_update_hotplug_bus() -> acpi_pcihp_eject_slot().

s390_pci_generate_plug_event()'s will still be generated, I guess this
is not an issue. The same thing would happen right now when unplugging
a device just before starting the guest.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190130155733.32742-7-david@redhat.com>
Reviewed-by: Collin Walling <walling@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>