NCT218 is compatible to NCT72 and NCT214. It also supports PEC (packet
error checking). Similar to NCT72 and NCT214, PEC support is undocumented.

Unlike NCT214 and NCT72, NCT218 does not support the undocumented secondary
chip and manufacturer ID registers at 0x3e and 0x3f and returns 0x00 when
reading those registers. The value for the chip revision register is not
documented but was observed to be 0xca. Use that information to improve
chip detection accuracy.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>