ARM: at91/dt: define sam9x5ek's crystal frequencies

Define sam9x5ek's main and slow crystal frequencies.
Signed-off-by: NBoris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: NNicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/at91sam9x5cm.dtsi

@@ -23,6 +23,14 @@
 		};
 	};
 
+	slow_xtal {
+		clock-frequency = <32768>;
+	};
+
+	main_xtal {
+		clock-frequency = <12000000>;
+	};
+
 	ahb {
 		apb {
 			pinctrl@fffff400 {