hwmon: (nct6775) Add support for NCT6798D

NCT6798D is, with the exception of fan and pwm channel configuration
registers, similar to other chips of the series. One interesting
difference is the chip ID, which is now extended to 13 bit (the 12-bit
chip ID value overlaps with the chip ID of NCT6797D).

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