usb: phy: generic: fix how we find out about our resources

instead of having each user of generic phy find
out about its own resources and pass it to the
core layer, have th core layer itself figure that
out. It's as simple as moving a piece of code
around. This fixes a big regression caused during
the merge window where am335x-based platforms
wouldn't be able to probe their PHY driver.

Signed-off-by: Felipe Balbi <balbi@ti.com>