ARM: dts: vf610: Align L2 cache-controller nodename with dtschema

Fix dtschema validator warnings like:
    l2-cache@40006000: $nodename:0:
        'l2-cache@40006000' does not match '^(cache-controller|cpu)(@[0-9a-f,]+)*$'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>