arm64: dts: allwinner: h6: add USB3 device nodes

Allwinner H6 SoC features USB3 functionality, with a DWC3 controller and
a custom PHY.

Add device tree nodes for them.

Signed-off-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>