hwmon: add Texas Instruments TPS23861 driver

Add basic monitoring support as well as port on/off control for Texas
Instruments TPS23861 PoE PSE IC.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20210121134434.2782405-2-robert.marko@sartura.hr
Signed-off-by: Guenter Roeck <linux@roeck-us.net>