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

Fix dtschema validator warnings like:
    l2-cache@22000: $nodename:0:
        'l2-cache@22000' does not match '^(cache-controller|cpu)(@[0-9a-f,]+)*$'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>