dt-bindings: clocksource: Add Oxford Semiconductor RPS Timer bindings

Add DT bindings for the Oxford Semiconductor RPS dual Timer.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/timer/oxsemi,rps-timer.txt

+Oxford Semiconductor OXNAS SoCs Family RPS Timer
+================================================
+
+Required properties:
+- compatible: Should be "oxsemi,ox810se-rps-timer"
+- reg : Specifies base physical address and size of the registers.
+- interrupts : The interrupts of the two timers
+- clocks : The phandle of the timer clock source
+
+example:
+
+timer0: timer@200 {
+	compatible = "oxsemi,ox810se-rps-timer";
+	reg = <0x200 0x40>;
+	clocks = <&rpsclk>;
+	interrupts = <4 5>;
+};