iio: adc: ad7380: add support for adaq4370-4 and adaq4380-4

iio: adc: ad7380: add support for adaq4370-4 and adaq4380-4

adaq4370-4 (2MSPS) and adaq4380-4 (4MSPS) are quad-channel precision data
acquisition signal chain μModule solutions compatible with the ad738x
family, with the following differences:

- pin selectable gain in front of each 4 adc
- internal reference is 3V derived from refin-supply (5V)
- additional supplies

This implies that IIO_CHAN_INFO_SCALE can not be shared by type for
these new 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-v4-4-864ff02babae@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>