dt-bindings: rtc: add stericsson,coh901331 bindings

Add device tree bindings for the ST-Ericsson COH 901 331 Real Time Clock
Signed-off-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>
Reviewed-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: NRob Herring <robh@kernel.org>

Documentation/devicetree/bindings/rtc/stericsson,coh901331.txt

+ST-Ericsson COH 901 331 Real Time Clock
+
+Required properties:
+- compatible: must be "stericsson,coh901331"
+- reg: address range of rtc register set.
+- interrupt-parent: phandle for the interrupt controller.
+- interrupts: rtc alarm interrupt.
+- clocks: phandle to the rtc clock source
+
+Example:
+	rtc: rtc@c0017000 {
+		compatible = "stericsson,coh901331";
+		reg = <0xc0017000 0x1000>;
+		interrupt-parent = <&vicb>;
+		interrupts = <10>;
+		clocks = <&rtc_clk>;
+	};