arm64: dts: allwinner: h6: PineH64 model B: Add wifi

PineH64 model B contains RTL8723CS wifi+bt combo module.

Since bluetooth support is not yet squared away, only wifi is enabled
for now.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Tested-by:  <clabbe.montjoie@gmail.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Link: https://lore.kernel.org/r/20201030172530.1096394-1-jernej.skrabec@siol.net