arm64: dts: marvell: add missing cache properties

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

  ac5-98dx35xx-rd.dtb: l2-cache: 'cache-unified' is a required property

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>