Add support for 6 temperature limit registers on IT8628E

Add support for 6 temperature limit registers on IT8628E

IT8628E has 6 temperature limit registers, overlayed with VIN7..VIN9
limit registers, but only 3 temperature offset registers. Given that,
introduce separate variables for the number of temperature limit
registers and the number of temperature offset registers.

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