dt-bindings: usb: dwc3: spacemit: add support for K3 SoC

Add compatible string for DWC3 USB controller found in SpacemiT K3 SoC.

The USB2.0 host controller in K3 SoC actually use DWC3 IP but only support
USB2.0 functionality, thus in the hardware layer, it has only one USB2 PHY.
While in K1 SoC, the USB controller has both USB2 and USB3 Combo PHY
connected, but able to work in a reduced USB2.0 mode which requres only
one USB2 PHY, leaves the USB3 Combo PHY to PCIe controller. So both K1
and K3 SoC are able to work in the USB2.0 mode which requires one PHY.

Explicitly reduce number of phy property to minimal one.

Signed-off-by: Yixun Lan <dlan@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20260320-02-k3-usb20-support-v2-1-308ea0e44038@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>