ARM: dts: Unify G2D device node with other devices on exynos4

G2D device is always available and doesn't depend on any external (board
specific) peripherals, so it can be unconditionally enabled.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>