ARM: Kirkwood: Enable USB 3.0 in kirkwood_defconfig

Some QNAP devices has a USB 3.0 host controller on a PCIe bus.  Enable
the driver for this in the default configuration.

Reported-by: Marek Vasut <marex@denx.de>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>