ARM64: dts: meson-gxl-nexbox-a95x: enable the USB controller

The Nexbox A95X provides two USB ports. Enable the SoC's USB controller
on this board to make these USB ports usable.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>