kobject/hotplug split

This splits the implicit generation of hotplug events from kobject_add() and kobject_del(), to give the driver core control over the time the event is created.

The kobject_register() and unregister functions still have the same behavior and emit the events by themselves.

The class, block and device core is changed now to emit the hotplug event _after_ the "dev" file, the "device" symlink and the default attributes are created. This will save udev from spinning in a stat() loop to wait for the files to appear, which is expensive if we have a lot of concurrent events.

Thanks for splitting this up. I've applied all 6 to my trees now.

greg k-h