hwmon: (nct6775) Introduce separate temperature labels for NCT6792 and NCT6793

NCT6792 and NCT6793 are mostly register compatible to NCT6791, but
temperature sources are different and difficult to manage with a single
temperature label array. Introduce separate temperature label arrays
for those chips to reflect the differences.

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