hwmon: Add Maxim MAX6620 hardware monitoring driver

Add hardware monitoring driver for Maxim MAX6620 Fan controller

Originally-from: L. Grunenberg <contact@lgrunenberg.de>
Originally-from: Cumulus Networks <support@cumulusnetworks.com>
Originally-from: Shuotian Cheng <shuche@microsoft.com>
Signed-off-by: Arun Saravanan Balachandran <Arun_Saravanan_Balac@dell.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>