dt/bindings: arm-boards: add binding for Versatile core module

Add binding for the core module found on ARM versatile AB and PB boards.
Signed-off-by: NRob Herring <robh@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NLinus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/arm/arm-boards

@@ -86,3 +86,9 @@ Interrupt controllers:
 	compatible = "arm,versatile-sic";
 	interrupt-controller;
 	#interrupt-cells = <1>;
+
+Required nodes:
+
+- core-module: the root node to the Versatile platforms must have
+  a core-module with regs and the compatible strings
+  "arm,core-module-versatile", "syscon"