dt-bindings: timer: C-SKY Multi-processor timer

Dt-bingdings doc for C-SKY SMP system setting.
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Documentation/devicetree/bindings/timer/csky,mptimer.txt

+============================
+C-SKY Multi-processors Timer
+============================
+
+C-SKY multi-processors timer is designed for C-SKY SMP system and the
+regs is accessed by cpu co-processor 4 registers with mtcr/mfcr.
+
+ - PTIM_CTLR "cr<0, 14>" Control reg to start reset timer.
+ - PTIM_TSR  "cr<1, 14>" Interrupt cleanup status reg.
+ - PTIM_CCVR "cr<3, 14>" Current counter value reg.
+ - PTIM_LVR  "cr<6, 14>" Window value reg to triger next event.
+
+==============================
+timer node bindings definition
+==============================
+
+	Description: Describes SMP timer
+
+	PROPERTIES
+
+	- compatible
+		Usage: required
+		Value type: <string>
+		Definition: must be "csky,mptimer"
+	- clocks
+		Usage: required
+		Value type: <node>
+		Definition: must be input clk node
+	- interrupts
+		Usage: required
+		Value type: <u32>
+		Definition: must be timer irq num defined by soc
+
+Examples:
+---------
+
+	timer: timer {
+		compatible = "csky,mptimer";
+		clocks = <&dummy_apb_clk>;
+		interrupts = <16>;
+		interrupt-parent = <&intc>;
+	};