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

Fix dtschema validator warnings like:
     l2-cache-controller@c4200000: $nodename:0:
         'l2-cache-controller@c4200000' does not match '^(cache-controller|cpu)(@[0-9a-f,]+)*$'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20200626080626.4080-1-krzk@kernel.org