ARM: dts: ox820: align interrupt controller node name with dtschema

Fixes dtbs_check warnings like:

  gic@1000: $nodename:0: 'gic@1000' does not match '^interrupt-controller(@[0-9a-f,]+)*$'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20220317115705.450427-1-krzysztof.kozlowski@canonical.com