[CLASS DEVICE]: add attribute_group creation

Extend the support of attribute groups in class_device's to allow
groups to be created as part of the registration process. This allows
network device's to avoid race between registration and creating
groups.

Note that unlike attributes that are a property of the class object,
the groups are a property of the class_device object. This is done
because there are different types of network devices (wireless for
example).

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>