hwmon: (lm63) Add additional sysfs group for temp2_type attribute

With the new hwmon API, we can only add groups of attributes, not individual
attributes. To prepare for the use of the new API, add an additional sensor
group for the temp2_type attribute and register it with sysfs_create_group
instead of device_create_file.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jean Delvare <jdelvare@suse.de>