arm64: dts: rockchip: add clk-480m for ehci and ohci of rk3399

arm64: dts: rockchip: add clk-480m for ehci and ohci of rk3399

We found that the suspend process was blocked when it run into
ehci/ohci module due to clk-480m of usb2-phy was disabled.

The root cause is that usb2-phy suspended earlier than ehci/ohci
(usb2-phy will be auto suspended if no devices plug-in). and the
clk-480m provided by it was diabled if no module used. However,
some suspend process related ehci/ohci are base on this clock,
so we should refer it into ehci/ohci driver to prevent this case.

Change-Id: Ic5e70a4234382e5cd1e1690e5174891e89360741
Signed-off-by: Frank Wang <frank.wang@rock-chips.com>