hwmon: (nct6683) Add basic support for NCT6683 on Mitac boards

Mitac microcode differs from Intel microcode. One key difference
is that pwm values can be written.

Detect vendor from customer ID field and no longer use DMI data
to identify which microcode is running on the chip.

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