phy: renesas: rcar-gen3-usb2: Add regulator for OTG VBUS control

phy: renesas: rcar-gen3-usb2: Add regulator for OTG VBUS control

Enable OTG VBUS control on R-Car Gen3 USB2 PHY by registering a regulator
driver that manages the VBOUT line. This change allows the controller to
handle VBUS output for OTG ports using the regulator framework when the
platform requires hardware-based VBUS control.

Without this, some platforms cannot properly manage VBUS power on OTG-
capable ports, leading to potential USB functionality issues.

Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Link: https://patch.msgid.link/6c1aebf60b4d8ff0c51a8243c68b397c1a384867.1766405010.git.tommaso.merciai.xr@bp.renesas.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>