ARM: at91/dt: introduce atmel,<chip>-dbgu

The DBGU is not a simple UART and we need to be able to distinguish it from the
other UARTs, in particular to get its address and check the chip id.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
diff --git a/arch/arm/boot/dts/at91sam9263.dtsi b/arch/arm/boot/dts/at91sam9263.dtsi
index fce301c..e07dae7 100644
--- a/arch/arm/boot/dts/at91sam9263.dtsi
+++ b/arch/arm/boot/dts/at91sam9263.dtsi
@@ -762,7 +762,7 @@
 			};
 
 			dbgu: serial@ffffee00 {
-				compatible = "atmel,at91sam9260-usart";
+				compatible = "atmel,at91sam9260-dbgu", "atmel,at91sam9260-usart";
 				reg = <0xffffee00 0x200>;
 				interrupts = <1 IRQ_TYPE_LEVEL_HIGH 7>;
 				pinctrl-names = "default";