Documentation: Add documentation for CCN-512 DTS binding

Indicate the arm-ccn perf back-end supports now ccn-512.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marek Bykowski <marek.bykowski@gmail.com>
Signed-off-by: Will Deacon <will@kernel.org>

Documentation/devicetree/bindings/perf/arm-ccn.txt

@@ -6,6 +6,7 @@ Required properties:
 	"arm,ccn-502"
 	"arm,ccn-504"
 	"arm,ccn-508"
+	"arm,ccn-512"
 
 - reg: (standard registers property) physical address and size
 	(16MB) of the configuration registers block