arm64: dts: rockchip: enable usb2 for RK3328 evaluation board

Rockchip's RK3328 evaluation board has one usb2 otg controller
and one usb2 host controller which consist of EHCI and OHCI.
Each usb controller connects with one usb2 phy port through
UTMI+ interface. Let's enable them to support usb2 on RK3328
evaluation board.

Signed-off-by: William Wu <william.wu@rock-chips.com>
[restructured enablement of u2phy subnodes]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>