usb: phy: Enable compile testing for some of drivers

Some of the USB phy drivers can be compile tested to increase build
coverage.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20191230172215.17370-2-krzk@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>