dt-bindings: Introduce soc sleep stats bindings for QTI SoCs

Add device binding documentation for Qualcomm Technology Inc's (QTI)
SoC sleep stats driver. The driver is used for displaying SoC sleep
statistic maintained by Always On Processor or Resource Power Manager.

Change-Id: I0ad338cef916969352bc552c53a19fbae8488836

bindings/soc/qcom/soc-sleep-stats.txt

@@ -0,0 +1,36 @@
+* SoC Sleep Stats
+
+Always On Processor/Resource Power Manager maintains statistics of the SoC
+sleep modes involving lowering or powering down of the backbone rails - Cx
+and Mx and the oscillator clock XO.
+
+Statistics includes SoC sleep mode type, number of times low power mode were
+entered, time of last entry, time of last exit and accumulated sleep duration.
+SoC Sleep Stats driver provides sysfs interface to display this information.
+
+Properties:
+
+- compatible:
+	Usage: required
+	Value type: <string>
+	Definition: Should be "qcom,rpmh-sleep-stats" or "qcom,rpm-sleep-stats".
+
+- reg:
+	Usage: required
+	Value type: <prop-encoded-array>
+	Definition: The base address on the Always On Processor or Resource Power
+		    Manager from where the stats are read.
+
+EXAMPLE 1:
+
+	rpmh_sleep_stats: soc-sleep-stats@c3f0000 {
+		compatible = "qcom,rpmh-sleep-stats";
+		reg = <0 0xc3f0000 0 0x400>;
+	};
+
+EXAMPLE 2:
+
+	rpm_sleep_stats: soc-sleep-stats@4690000 {
+		compatible = "qcom,rpm-sleep-stats";
+		reg = <0 0x04690000 0 0x400>;
+	};