hwmon: (pmbus/zl6100) Update documentation for zl6100 driver

Update documentation for zl6100 driver and fix dead links to technical
specifications

Signed-off-by: Erik Rosen <erik.rosen@metormote.com>
Link: https://lore.kernel.org/r/20210423153329.33457-3-erik.rosen@metormote.com


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