usb: xhci: plat: Add USB phy support

The Marvell Armada 385 AP needs a dumb phy in order to enable the USB3 VBUS.

Add a call to retrieve a USB PHY to XHCI plat in order to support this.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>