Add documentation of device tree bindings to support
sigma delta modulator in IIO framework.
Signed-off-by: NArnaud Pouliquen <arnaud.pouliquen@st.com>
Acked-by: NRob Herring <robh@kernel.org>
Acked-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: NMark Brown <broonie@kernel.org>