bindings: arm: msm: Add documentation for subsystem sleep_stats_driver

This change adds bindings for subsystem_sleep_stats
driver.

Change-Id: Icf3d32ad8be0541cc6821f8a8c6bf9cf8dea5a0a

bindings/arm/msm/subsystem-sleep-stats.yaml

@@ -0,0 +1,31 @@
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/bindings/arm/msm/subsystem-sleep-stats.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: The document describes the device tree binding for subsystem-sleep-stats
+
+maintainers:
+  - Tushar Nimkar <tnimkar@codeaurora.org>
+
+description: |+
+  Differet Subsystems maintains stats data in SMEM.
+  It tells about the individual subsystem information at any given
+  time like system sleep counts, system sleep last entered at
+  and accumulated duration etc. This drive provide a IOCTL way
+  to read those stats from respective SMEMs.
+
+The required properties for subsystem stats driver is:
+
+properties:
+ compatible:
+   Usage: required
+   Value type: <string>
+   Definition: Should be "qcom,subsystem-sleep-stats".
+
+
+example:
+  - |
+    subsystem-sleep-stats {
+		compatible = "qcom,subsystem-sleep-stats";
+	};