dt-bindings: timer: Document RDA8810PL SoC timer

Document RDA Micro RDA8810PL SoC timer.
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Documentation/devicetree/bindings/timer/rda,8810pl-timer.txt

+RDA Micro RDA8810PL Timer
+
+Required properties:
+- compatible      :  "rda,8810pl-timer"
+- reg             :  Offset and length of the register set for the device.
+- interrupts      :  Should contain two interrupts.
+- interrupt-names :  Should be "hwtimer", "ostimer".
+
+Example:
+
+		apb@20900000 {
+			compatible = "simple-bus";
+			...
+			timer@10000 {
+				compatible = "rda,8810pl-timer";
+				reg = <0x10000 0x1000>;
+				interrupts = <16 IRQ_TYPE_LEVEL_HIGH>,
+					     <17 IRQ_TYPE_LEVEL_HIGH>;
+				interrupt-names = "hwtimer", "ostimer";
+			};