s390/qeth: use dev->groups for common sysfs attributes

All qeth devices have a minimum set of sysfs attributes, and non-OSN
devices share a group of additional attributes. Depending on whether
the device is forced to use a specific discipline, the device_type then
specifies further attributes.

Shift the common attributes into dev->groups, so that the device_type
only contains the discipline-specific attributes. This avoids exposing
the common attributes to the disciplines, and nicely cleans up our
sysfs code.

While replacing the qeth_l*_*_device_attributes() helpers, switch from
sysfs_*_groups() to the more generic device_*_groups().

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>