dt-bindings: reset: renesas,rzg2l-usbphy-ctrl: Document RZ/V2L USBPHY Control bindings

Add device tree binding document for RZ/V2L USBPHY Control Device.
RZ/V2L USBPHY Control Device is identical to one found on the RZ/G2L SoC.
No driver changes are required as generic compatible string
"renesas,rzg2l-usbphy-ctrl" will be used as a fallback.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220227230302.30388-1-prabhakar.mahadev-lad.rj@bp.renesas.com