dt-bindings: add device bindings for DDR stats node

DDR statistics are exported by the always-on subsystem and can be read
from Linux. Add device bindings to setup the device node to read the
location and output the contents.

Change-Id: Id736933a6fd647ecad3daa2e57d97247c6d45c8f

bindings/arm/msm/ddr_stats.txt

@@ -0,0 +1,32 @@
+* DDR Stats
+
+AOP maintains DDR statistics like DDR LPMs and frequency stats. DDR stats
+driver gives sysfs interface to display this.
+
+PROPERTIES
+
+- compatible:
+	Usage: required
+	Value type: <string>
+	Definition: Should be "qcom,ddr-stats".
+
+- reg:
+	Usage: required
+	Value type: <prop-encoded-array>
+	Definition: The address on the AOP Message RAM from where the stats
+		    are read should be provided as "phys_addr_base".
+		    The offset from which the stats are available should be
+		    provided as "offset_addr".
+
+- reg-names:
+	Usage: required
+	Value type: <prop-encoded-array>
+	Definition: Provides labels for the reg property.
+
+EXAMPLE:
+	qcom,ddr-stats@c300000 {
+		compatible = "qcom,ddr-stats";
+		reg = <0xc300000 0x1000>, <0xc3f001c 0x4>;
+		reg-names = "phys_addr_base", "offset_addr";
+	};
+