arm64: dts: allwinner: h6: Enable SPDIF for Beelink GS1

Beelink GS1 board has a SPDIF out connector, so enable it in
the device-tree and add a simple SPDIF soundcard.

Signed-off-by: Clément Péron <peron.clem@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>