dt-bindings: arm,coresight-cti: Add missing additionalProperties on child nodes

Just as unevaluatedProperties or additionalProperties are required at
the top level of schemas, they should (and will) also be required for
child node schemas. That ensures only documented properties are
present for any node.

Adding additionalProperties constraint on 'trig-conns' nodes results in
warnings that 'cpu' and 'arm,cs-dev-assoc' are not allowed. These are
already defined for the parent node, but need to be duplicated for the
child node. Drop the free form description that the properties also apply
to the child nodes.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Link: https://lore.kernel.org/r/20230925220511.2026514-2-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>