hw/pci: switch to a generic hotplug handling for PCIDevice

hw/pci: switch to a generic hotplug handling for PCIDevice

make qdev_unplug()/device_set_realized() to call hotplug handler's
plug/unplug methods if available and remove not needed anymore
hot(un)plug handling from PCIDevice.

In case if hotplug handler is not available, revert to the legacy
hotplug method for compatibility with not yet converted buses.

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>