Documentation/devicetree/bindings: add documentation for the APM X-Gene SoC RTC DTS binding

Signed-off-by: NRameshwar Prasad Sahu <rsahu@apm.com>
Signed-off-by: NLoc Ho <lho@apm.com>
Cc: Jon Masters <jcm@redhat.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/devicetree/bindings/rtc/xgene-rtc.txt

+* APM X-Gene Real Time Clock
+
+RTC controller for the APM X-Gene Real Time Clock
+
+Required properties:
+- compatible : Should be "apm,xgene-rtc"
+- reg: physical base address of the controller and length of memory mapped
+  region.
+- interrupts: IRQ line for the RTC.
+- #clock-cells: Should be 1.
+- clocks: Reference to the clock entry.
+
+Example:
+
+rtcclk: rtcclk {
+	compatible = "fixed-clock";
+	#clock-cells = <1>;
+	clock-frequency = <100000000>;
+	clock-output-names = "rtcclk";
+};
+
+rtc: rtc@10510000 {
+	compatible = "apm,xgene-rtc";
+	reg = <0x0 0x10510000 0x0 0x400>;
+	interrupts = <0x0 0x46 0x4>;
+	#clock-cells = <1>;
+	clocks = <&rtcclk 0>;
+};