kset: add kset_create_and_add function

Now ksets can be dynamically created on the fly, no static definitions
are required.  Thanks to Miklos for hints on how to make this work
better for the callers.

And thanks to Kay for finding some stupid bugs in my original version
and pointing out that we need to handle the fact that kobject's can have
a kset as a parent and to handle that properly in kobject_add().

Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>