ARM: at91/dt: ethernut5: define crystals frequencies

Define egnite Ethernut 5 main and slow crystals frequencies.
Signed-off-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: NNicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/ethernut5.dts

@@ -20,6 +20,16 @@
 		reg = <0x20000000 0x08000000>;
 	};
 
+	clocks {
+		slow_xtal {
+			clock-frequency = <32768>;
+		};
+
+		main_xtal {
+			clock-frequency = <18432000>;
+		};
+	};
+
 	ahb {
 		apb {
 			dbgu: serial@fffff200 {