dt-bindings: phy: add rockchip usbdp combo phy document

dt-bindings: phy: add rockchip usbdp combo phy document

Add device tree binding document for Rockchip USBDP Combo PHY
with Samsung IP block.

Co-developed-by: Frank Wang <frank.wang@rock-chips.com>
Signed-off-by: Frank Wang <frank.wang@rock-chips.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20240408225109.128953-2-sebastian.reichel@collabora.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>