dt-bindings: reset: renesas,rzv2h-usb2phy: Add '#mux-state-cells' property

dt-bindings: reset: renesas,rzv2h-usb2phy: Add '#mux-state-cells' property

Add the '#mux-state-cells' property to support describing the USB VBUS_SEL
multiplexer as a mux-controller in the Renesas RZ/V2H(P) USB2PHY binding.

The mux-controller cannot be integrated into the parent USB2PHY node
because the VBUS source selector is part of a separate hardware block,
not the USB2PHY block itself.

This is required to properly configure USB PHY power selection on
RZ/V2H(P) and RZ/G3E SoCs.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>