dt-bindings: phy: renesas,usb2-phy: Document RZ/G2UL phy bindings

Document USB phy bindings for RZ/G2UL SoC. RZ/G2UL USB phy is identical to
one found on the RZ/G2L SoC. No driver changes are required as generic
compatible string "renesas,rzg2l-usb2-phy" will be used as a fallback.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220423134752.143090-1-biju.das.jz@bp.renesas.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>