dt-bindings: hwmon: Add TI TPS23861 bindings

Document bindings for the Texas Instruments TPS23861 driver.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210121134434.2782405-1-robert.marko@sartura.hr
Signed-off-by: Guenter Roeck <linux@roeck-us.net>