dt-bindings: usb: renesas,usbhs: Document RZ/V2L bindings

Document RZ/V2L (R9A07G054) SoC bindings. USBHS block is identical to one
found on RZ/A2 SoC. No driver changes are required as generic compatible
string "renesas,rza2-usbhs" 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>
Acked-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220227231531.32279-1-prabhakar.mahadev-lad.rj@bp.renesas.com