Add support for the IT8716F (prefix it8716). It is mostly similar to the
IT8712F so there's not much to do. The most significant difference is that
fan speeds are now reported as 16-bit values, without fan clock dividers.
For this reason, I made the fan_divs optional in sensors. I also made the
fans themselves optional, as I noticed that a number of motherboards don't
use (and don't enable) fan3.
I've made a separate section (chip "it8716-*") in sensors.conf.eg, because
new motherboards tend to have different wirings (e.g. negative voltage
lines are not monitored) so this will make for saner defaults.
Thanks to Stian Oksavik for testing.
