Simplify code and reduce code size by using the new hwmon
registration API.

Other changes:

- Convert to use regmap, and drop local caching. This avoids reading
  registers unnecessarily, and uses regmap for caching of non-volatile
  registers.
- Add support for temp2_max, temp2_max_alarm, temp2_max_hyst, and
  temp2_offset.
- Order include files alphabetically
- Drop FSF address
- Check errors from register read and write functions and report
  to userspace.
- Accept negative hysteresis values. While unlikely, a maximum limit
  _can_ be set to a value smaller than 31 degrees C, which makes negative
  hysteresis values possible.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>