dt-bindings: thermal: cooling-devices: Add missing cache related properties

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

Acked-by: Amit Kucheria <amitk@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221104162450.1982114-1-robh@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>