On rockchip devices vbus is supplied by a separate power supply, often
through a regulator. Add support for describing the the regulator in
device-tree following the same convention as several other usb phy's.
Signed-off-by: NSjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: NKishon Vijay Abraham I <kishon@ti.com>