allwinner: a523: Enable I2S and SPDIF TX

Merge series from Chen-Yu Tsai <wens@kernel.org>:

This series enables the SPDIF and I2S hardware found on the Allwinner
A523/A527/T527 family SoCs. These SoCs have one SPDIF interface and
four I2S interfaces. All of them are capable of both playback and
capture, however the SPDIF driver only supports playback.