iio: ad7380: add support for SPI offload

Add support for SPI offload to the ad7380 driver. SPI offload allows
sampling data at the max sample rate (2MSPS with one SDO line).

This is developed and tested against the ADI example FPGA design for
this family of ADCs [1].

[1]: http://analogdevicesinc.github.io/hdl/projects/ad738x_fmc/index.html

Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
Link: https://patch.msgid.link/20250310-wip-bl-spi-offload-ad7380-v4-1-b184b37b7c72@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: spectrum70

drivers/iio/adc/Kconfig

@@ -228,7 +228,9 @@ config AD7298
 config AD7380
 	tristate "Analog Devices AD7380 ADC driver"
 	depends on SPI_MASTER
+	select SPI_OFFLOAD
 	select IIO_BUFFER
+	select IIO_BUFFER_DMAENGINE
 	select IIO_TRIGGER
 	select IIO_TRIGGERED_BUFFER
 	help