driver: adc: ad405x: Add RTIO stream

Added support for RTIO stream.
Also added sampling_period property to the DTS. This is for setting the
sampling period when streaming is used.
Hardware or kernel timer can be
used for this.
To use hardware timer you need to add it to the DTS. Example:

{
	chosen {
		zephyr,adc-clock = &counter0;
	};
};

Signed-off-by: Vladislav Pejic <vladislav.pejic@orioninc.com>

Author: vladislav-pejic

drivers/adc/Kconfig.ad405x

@@ -11,6 +11,13 @@ config ADC_AD405X
 	help
 	  Enable ADC driver for ADI AD405X.
 
+config AD405X_STREAM
+	bool "Use FIFO to stream data"
+	select AD405X_TRIGGER
+	depends on SPI_RTIO
+	help
+	  Use this configuration option to enable streaming ADC data via RTIO.
+
 config AD405X_TRIGGER
 	bool "AD405X interrupts"
 	default n