hwmon: add driver for the Microchip LAN966x SoC

Add support for the temperatur sensor and the fan controller on the
Microchip LAN966x SoC. Apparently, an Analog Bits PVT sensor is used
which can measure temperature and process voltages. But only a forumlae
for the temperature sensor is known. Additionally, the SoC support a fan
tacho input as well as a PWM signal to control the fan.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220401214032.3738095-5-michael@walle.cc


[groeck: Added missing reference in Documentation/hwmon/index.rst]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>