dt-bindings: add ARMv8 PMU binding

Add missing "arm,armv8-pmuv3" compatible property for ARMv8 PMU.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>

Documentation/devicetree/bindings/arm/pmu.txt

@@ -7,6 +7,7 @@ representation in the device tree should be done as under:-
 Required properties:
 
 - compatible : should be one of
+	"arm,armv8-pmuv3"
 	"arm,cortex-a15-pmu"
 	"arm,cortex-a9-pmu"
 	"arm,cortex-a8-pmu"