Documentation: dt: iio: at91-sama5d2_adc: add hw trigger edge binding

Add property for the edge type of the hardware trigger pin ADTRG
Signed-off-by: NEugen Hristev <eugen.hristev@microchip.com>
Acked-by: NRob Herring <robh@kernel.org>
Acked-by: NLudovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/at91-sama5d2_adc.txt

@@ -11,6 +11,11 @@ Required properties:
   - atmel,min-sample-rate-hz: Minimum sampling rate, it depends on SoC.
   - atmel,max-sample-rate-hz: Maximum sampling rate, it depends on SoC.
   - atmel,startup-time-ms: Startup time expressed in ms, it depends on SoC.
+  - atmel,trigger-edge-type: One of possible edge types for the ADTRG hardware
+  trigger pin. When the specific edge type is detected, the conversion will
+  start. Possible values are rising, falling, or both.
+  This property uses the IRQ edge types values: IRQ_TYPE_EDGE_RISING ,
+  IRQ_TYPE_EDGE_FALLING or IRQ_TYPE_EDGE_BOTH
 
 Example:
 
@@ -25,4 +30,5 @@ adc: adc@fc030000 {
 	atmel,startup-time-ms = <4>;
 	vddana-supply = <&vdd_3v3_lp_reg>;
 	vref-supply = <&vdd_3v3_lp_reg>;
+	atmel,trigger-edge-type = <IRQ_TYPE_EDGE_BOTH>;
 }