usb: phy: r-car gen2: use usb_add_phy_dev

Use usb_add_phy_dev instead of usb_add_phy, so that devices can
be bound to the phy. This is needed to set up USB phy for
some internal PCI USB host controllers on R-Car Gen2.

Signed-off-by: Valentine Barshak <valentine.barshak@cogentembedded.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>