dt-bindings: reset: renesas,rzg2l-usbphy-ctrl: Document USB VBUS regulator

The VBUS enable can be controlled by the VBOUT bit of the VBUS control
register. This register is part of usbphy-ctrl IP.

Document the USB VBUS regulator object.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20240702180032.207275-2-biju.das.jz@bp.renesas.com


Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>