hwmon: (dme1737) Add support for the SMSC SCH5027

Add support for the SCH5027. The differences to the DME1737 are:
- No support for programmable temp offsets
- In auto mode, PWM outputs stay on min value if temp goes below low threshold
  and can't be programmed to fully turn off
- Different voltage scaling
- No VID input

Signed-off-by: Juerg Haefliger <juergh@gmail.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>