driver core: allow non-root users to listen to uevents

Users can read sysfs files, there is no reason they should not be
allowed to listen to uevents.  This lets xorg and other userspace
programs properly get these messages without having to be root.

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