arm64: dts: exynos: Add unit address to soc node on Exynos5433

Add @0 unit address to 'soc' node match its 'reg' property and silence
DTC warning:

    Warning (unit_address_vs_reg): /soc: node has a reg or ranges property, but no unit name

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>