phy: rockchip-usb: introduce a common data-struct for the device

This introduces a common struct that holds data belonging to
the umbrella device that contains all the phys and that we
want to use later.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>