dt-bindings: introduce Command DB for QCOM SoCs

Command DB provides information on shared resources like clocks,
regulators etc., probed at boot by the remote subsytem and made
available in shared memory.

Cc: [e-mail]
Signed-off-by: Mahesh Sivasubramanian <[e-mail]>
Signed-off-by: Lina Iyer <[e-mail]>
Reviewed-by: Bjorn Andersson <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Reviewed-by: Stephen Boyd <[e-mail]>
Reviewed-by: Evan Green <[e-mail]>
Signed-off-by: Andy Gross <[e-mail]>

Documentation/devicetree/bindings/reserved-memory/qcom,cmd-db.txt

···
+Command DB
+---------
+
+Command DB is a database that provides a mapping between resource key and the
+resource address for a system resource managed by a remote processor. The data
+is stored in a shared memory region and is loaded by the remote processor.
+
+Some of the Qualcomm Technologies Inc SoC's have hardware accelerators for
+controlling shared resources. Depending on the board configuration the shared
+resource properties may change. These properties are dynamically probed by the
+remote processor and made available in the shared memory.
+
+The bindings for Command DB is specified in the reserved-memory section in
+devicetree. The devicetree representation of the command DB driver should be:
+
+Properties:
+- compatible:
+	Usage: required
+	Value type: <string>
+	Definition: Should be "qcom,cmd-db"
+
+- reg:
+	Usage: required
+	Value type: <prop encoded array>
+	Definition: The register address that points to the actual location of
+		    the Command DB in memory.
+
+Example:
+
+	reserved-memory {
+		[...]
+		reserved-memory@85fe0000 {
+			reg = <0x0 0x85fe0000 0x0 0x20000>;
+			compatible = "qcom,cmd-db";
+			no-map;
+		};
+	};