USB: phy: drop legacy board-file support

The legacy interface for associating controllers with phys from board
files and platform code has been unused since commit 9080b8dc

 ("ARM:
OMAP2+: Remove legacy usb-host.c platform init code"). Since then, all
calls to usb_get_phy_dev() and its devres version have been returning
-ENODEV.

Now that the final calls to these functions have been removed, we can
drop this legacy lookup interface altogether.

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>