usb: chipidea: Refactor USB PHY selection and keep a single PHY

Refactor the code in charge of looking up the USB PHY when no platdata
is provided. Attempt to get a generic USB PHY first, then look for a
legacy USB PHY through device-tree and finally get any registered PHY
with the correct type.

This way, only a single USB PHY is obtained and the flow is easier to
understand and follow.

All error pointers (except for EPROBE_DEFER) are considered as PHY
not found.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>