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

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

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200626080552.3627-1-krzk@kernel.org


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>