dt-bindings: cpufreq: qcom: Add missing cache related properties

The examples' cache nodes are incomplete as 'cache-unified' and
'cache-level' are required cache properties.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>