usb: musb: jz4740: obtain USB PHY from devicetree

Fall back to devm_usb_get_phy() if devicetree is not available.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>