ARM64: dts: meson-gxbb-p20x: Enable USB Nodes

Enable both gxbb USB controller and add a 5V regulator for the OTG port
VBUS

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
[khilman: rename vbus node to match P200 schematics]
Signed-off-by: Kevin Hilman <khilman@baylibre.com>