hwmon: (ntc_thermistor) Convert to new hwmon API

Use devm_hwmon_device_register_with_info() instead of
devm_hwmon_device_register_with_groups() to register the hwmon
device to simplify the code and make it easier to maintain.
As part of this change, thermal device registration is moved into
the hwmon core.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>