dt-bindings: sound: sun4i-i2s: add Allwinner R40 I2S compatible

Allwinner R40 has 3 I2S controllers, compatible to those, found in H3.

Add R40/H3 compatible pair to DT bindings.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210912072914.398419-2-jernej.skrabec@gmail.com