regulator: max77857: Add ADI MAX77857/59/MAX77831 Regulator bindings

Add ADI MAX77857/59 and MAX77831 Regulator device tree document.

Signed-off-by: Okan Sahin <okan.sahin@analog.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230717050736.10075-2-okan.sahin@analog.com


Signed-off-by: Mark Brown <broonie@kernel.org>