ASoC: sun4i-i2s: Document H3 with missing RX channel possibility

Like A83T the Allwinner H3 doesn't have the DMA reception available for
some audio interfaces.

As it's already documented for A83T convert this to an enum and add the H3
interface.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Clément Péron <peron.clem@gmail.com>
Link: https://lore.kernel.org/r/20201030144648.397824-15-peron.clem@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>