hwmon: (lm90) Create most optional attributes with sysfs_create_group

With the new hwmon API, all attributes have to be created as groups.
Use sysfs_create_group and sysfs_remove_group instead of device_create_file
and device_remove_file to prepare for the new API.

Exception is the 'pec' attribute which will stay with the i2c device.

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