hwmon: (it87) Add support for IT8689E

hwmon: (it87) Add support for IT8689E

Add support for the ITE IT8689E Super I/O chip. The IT8689E supports
newer autopwm, 12mV ADC, 16-bit fans, six fans, six PWM channels,
PWM frequency 2, six temperature inputs, AVCC3, temperature offset,
and fan on/off control.

Give it8689 its own GPIO configuration block in it87_find() rather
than sharing the it8620/it8628 block. The shared block reads
IT87_SIO_PINX2_REG and either marks IN3 as internal AVCC or skips
IN9. Because it8689 declares FEAT_AVCC3, IN9 is already marked as
always-internal before the GPIO block is reached; applying the PINX2
check would either create duplicate AVCC labels on IN3 and IN9 or
incorrectly skip IN9.

Also update Documentation/hwmon/it87.rst and drivers/hwmon/Kconfig to
document the newly supported chip.

Signed-off-by: Markus Hoffmann <markus@thehoffs.at>
Link: https://lore.kernel.org/r/20260322103301.18112-1-markus@thehoffs.at
Signed-off-by: Guenter Roeck <linux@roeck-us.net>