ARM64: dts: meson-gxl-s905x-p212: Add phy-supply for usb0

Like LibreTech-CC, the USB0 needs the 5V regulator to be enabled to power the
devices on the P212 Reference Design based boards.

Fixes: b9f07cb4

 ("ARM64: dts: meson-gxl-s905x-p212: enable the USB controller")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>