ARM: dts: berlin: Align L2 cache-controller nodename with dtschema

Fix dtschema validator warnings like:
    l2-cache-controller@ac0000: $nodename:0:
        'l2-cache-controller@ac0000' does not match '^(cache-controller|cpu)(@[0-9a-f,]+)*$'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Link: https://lore.kernel.org/r/20200626080642.4244-1-krzk@kernel.org

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>