ARM: dts: Enable USB gadget functionality for exynos4210-trats

This patch adds device tree nodes necessary to enable USB
gadget functionality on Exynos4210-based Trats board.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>