ARM: dts: at91: at91sam9x5ek: use DMA for USART0

Use DMA for USART0 (which is used as ttyS1) as we have enough channels and to
show how to specify DMA use with serial nodes.

Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

arch/arm/boot/dts/at91sam9x5ek.dtsi

@@ -50,6 +50,8 @@
 			};
 
 			usart0: serial@f801c000 {
+				atmel,use-dma-rx;
+				atmel,use-dma-tx;
 				status = "okay";
 			};