hwmon: (lm90) Enable full PEC support for ADT7461A

Experiments show that ADT7461A and NCT1008 support PEC, even though it is
not documented. Enable support for it in the driver. Since ADT7461 only
supports partial PEC, this means that the configuration for ADT7461A
needs to be separated from ADT7461.

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