usb: dwc3: Add optional VBUS regulator support to SpacemiT K1

usb: dwc3: Add optional VBUS regulator support to SpacemiT K1

Some SpacemiT K1 boards (like OrangePi R2S) provide USB VBUS
through a controllable regulator. Add support for the optional
vbus-supply property so the regulator can be properly managed
in host mode instead of left always-on. Note that this doesn't
apply to USB Hub downstream ports with different VBUS supplies.

The enabled and disabled actions of the regulator are handled
automatically by devm_regulator_get_enable_optional().

Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>
Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Reviewed-by: Anand Moon <linux.amoon@gmail.com>
Link: https://patch.msgid.link/20260326100010.3588454-2-amadeus@jmu.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>