ARM: dts: Enabling ehci-s5p driver for EXYNOS5250

Adding EHCI device tree node for Exynos5250 along with
the device base adress and gpio line for vbus.

Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>