ARM: dts: exynos: Add G3D power domain to Exynos542x

Add a power domain for G3D/Mali device present in Exynos542x/5800 SoCs.
Node for the Mali device will be added by a separate patch.

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