usb: chipidea: permit driver bindings pass phy pointer

Sometimes, the driver bindings may know what phy they use.
For example, when using device tree, the usb controller may have a
phandler pointing to usb phy.

Signed-off-by: Richard Zhao <richard.zhao@freescale.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Acked-by: Felipe Balbi <balbi@ti.com>
Tested-by: Subodh Nijsure <snijsure@grid-net.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>