dt-bindings: arm: cpus: Add ASPEED SMP

The AST2600 SoC contains two CPUs and requires the operating system to
bring the second one out of firmware.

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>

Documentation/devicetree/bindings/arm/cpus.yaml

@@ -175,6 +175,7 @@ properties:
               - amlogic,meson8-smp
               - amlogic,meson8b-smp
               - arm,realview-smp
+              - aspeed,ast2600-smp
               - brcm,bcm11351-cpu-method
               - brcm,bcm23550
               - brcm,bcm2836-smp