arm64: dts: broadcom: add missing cache properties

As all level 2 and level 3 caches are unified, add required
cache-unified properties to fix warnings like:

  bcm94908.dtb: l2-cache0: 'cache-unified' is a required property

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: William Zhang <william.zhang@broadcom.com>
Link: https://lore.kernel.org/r/20230421223208.115555-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>