ARM: dts: meson: move the L2 cache-controller inside the SoC node

All IO mapped SoC peripherals should be within the "soc" node. Move the
L2 cache-controller there as well since it's the only one not following
this pattern.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20200815182223.408965-1-martin.blumenstingl@googlemail.com