regulator: dt-bindings: maxim,max77843: Add MAX77843 bindings

Document the bindings for MAX77843 regulator driver.  The bindings are
almost identical to MAX77693 bindings, except the actual names of
regulators.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220111174805.223732-4-krzysztof.kozlowski@canonical.com