dt-bindings/clocksource: Add Spreadtrum SC9860 timer documentation

This patch adds documentation of device tree bindings for the timers
found on the Spreadtrum SC9860 platform.
Signed-off-by: Baolin Wang <baolin.wang@spreadtrum.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: devicetree@vger.kernel.org
Link: http://lkml.kernel.org/r/1515418139-23276-7-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

Documentation/devicetree/bindings/timer/spreadtrum,sprd-timer.txt

+Spreadtrum timers
+
+The Spreadtrum SC9860 platform provides 3 general-purpose timers.
+These timers can support 32bit or 64bit counter, as well as supporting
+period mode or one-shot mode, and they are can be wakeup source
+during deep sleep.
+
+Required properties:
+- compatible: should be "sprd,sc9860-timer" for SC9860 platform.
+- reg: The register address of the timer device.
+- interrupts: Should contain the interrupt for the timer device.
+- clocks: The phandle to the source clock (usually a 32.768 KHz fixed clock).
+
+Example:
+	timer@40050000 {
+		compatible = "sprd,sc9860-timer";
+		reg = <0 0x40050000 0 0x20>;
+		interrupts = <GIC_SPI 26 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&ext_32k>;
+	};