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: Rob Herring <[e-mail]>
Cc: Pawel Moll <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Ian Campbell <[e-mail]>
Cc: Kumar Gala <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Acked-by: Linus Walleij <[e-mail]>

Documentation/devicetree/bindings/arm/arm-boards

···
 	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"