ARM: SoC: Add virtual GIC interface DT bindings to exynos5250

The exynoes5250 chips have a fully Cortex-A15 compatible GIC v2.0 with
virtualization support embedded in them. Let KVM use these features.

Signed-off-by: Christoffer Dall <c.dall@virtualopensystems.com>

Conflicts:
	arch/arm/boot/dts/exynos5250.dtsi