dt-bindings: iio: adc: Add max11205 documentation file

Add bindings documentation file and MAINTAINERS entry for MAX11205.

Signed-off-by: Ramona Bolboaca <ramona.bolboaca@analog.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220831133021.215625-1-ramona.bolboaca@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>