ARM: dts: OMAP4: Add omap-usb2 data

Add omap-usb2 data node in omap4 device tree file. Since omap-usb2
is connected to ocp2scp, omap-usb2 dt data is added as a child node
of ocp2scp. The information about this data node is availabe @
Documentation/devicetree/bindings/usb/usb-phy.txt

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>