dt-bindings: opp: opp-v2-kryo-cpu: Add missing 'cache-unified' property in example

The examples' cache nodes are incomplete as 'cache-unified' is a
required cache property for unified caches which an L2 cache certainly
is.

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>