arm64: dts: intel: socfpga_agilex: move usbphy out of soc node

The usual usb-nop-xceiv USB phy node should be under root node, to fix
dtc warning:

    arch/arm64/boot/dts/intel/socfpga_agilex.dtsi:472.21-476.5:
        Warning (simple_bus_reg): /soc/usbphy@0: missing or empty reg/ranges property

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>