kobject: replace '/' with '!' in name

Some (block) devices have a '/' in the name, and need special
handling. Let's have that rule to the core, so we can remove it
from the block class.

Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>