Implement the sysfs attributes directly in the driver for
shutdown threshold temperature and pass an extra attribute group
to the hwmon core when registering the hwmon device.

Link: https://lore.kernel.org/netdev/20230815045658.80494-12-michael.chan@broadcom.com/
 Cc: Jean Delvare <jdelvare@suse.com>
 Cc: Guenter Roeck <linux@roeck-us.net>
 Cc: linux-hwmon@vger.kernel.org
Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>