Driver core: allow to delay the uevent at device creation time

For the block subsystem, we want to delay all uevents until the
disk has been scanned and allpartitons are already created before
the first event is sent out.

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