ARM: dts: Enable support for generic USB DRD phy for exynos5250

Add device tree node for new usbdrd-phy driver, which
is based on generic phy framework.

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>