docs: iio: ad7380: add adaq4370-4 and adaq4380-4

Adding documentation for adaq4370-4 and adaq4380-4 supported devices. In
particular, document the reference voltage mechanism and the gain
parameter that are specific to adaq devices.

Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20241030-ad7380-add-adaq4380-4-support-v4-5-864ff02babae@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: justeph

Documentation/iio/ad7380.rst

@@ -27,6 +27,8 @@ The following chips are supported by this driver:
 * `AD7386-4 <https://www.analog.com/en/products/ad7386-4.html>`_
 * `AD7387-4 <https://www.analog.com/en/products/ad7387-4.html>`_
 * `AD7388-4 <https://www.analog.com/en/products/ad7388-4.html>`_
+* `ADAQ4370-4 <https://www.analog.com/en/products/adaq4370-4.html>`_
+* `ADAQ4380-4 <https://www.analog.com/en/products/adaq4380-4.html>`_
 
 
 Supported features
@@ -47,6 +49,12 @@ ad7380-4
 ad7380-4 supports only an external reference voltage (2.5V to 3.3V). It must be
 declared in the device tree as ``refin-supply``.
 
+ADAQ devices
+~~~~~~~~~~~~
+
+adaq4370-4 and adaq4380-4 don't have an external reference, but use a 3.3V
+internal reference derived from one of its supplies (``refin-supply``)
+
 All other devices from ad738x family
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -121,6 +129,14 @@ Example for AD7386/7/8 (2 channels parts):
 
 When enabling sequencer mode, the effective sampling rate is divided by two.
 
+Gain (ADAQ devices only)
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+ADAQ devices have a pin selectable gain in front of each ADC. The appropriate
+gain is selectable from device tree using the ``adi,gain-milli`` property.
+Refer to the typical connection diagrams section of the datasheet for pin
+wiring.
+
 Unimplemented features
 ----------------------