ARM: mxs: retrieve timer irq from device tree

Rather than using the static timer irq definition, we should retrieve
timer irq from device tree for better.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
diff --git a/arch/arm/boot/dts/imx23.dtsi b/arch/arm/boot/dts/imx23.dtsi
index e613831..573066b 100644
--- a/arch/arm/boot/dts/imx23.dtsi
+++ b/arch/arm/boot/dts/imx23.dtsi
@@ -389,8 +389,9 @@
 			};
 
 			timrot@80068000 {
+				compatible = "fsl,imx23-timrot", "fsl,timrot";
 				reg = <0x80068000 0x2000>;
-				status = "disabled";
+				interrupts = <28 29 30 31>;
 			};
 
 			auart0: serial@8006c000 {