phy: rockchip-inno-usb2: add support of usb2-phy for rv1108 SoCs

This adds support usb2-phy for rv1108 SoCs and amend phy Documentation.

Signed-off-by: Frank Wang <frank.wang@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>