ARM: dts: Enable support for DWC3 controller for exynos5420

Add device tree nodes for DWC3 controller present on
Exynos 5420 SoC, to enable support for USB 3.0.

Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>