ASoC: mchp-spdiftx: add driver for S/PDIF TX Controller

The new SPDIF TX controller is a serial port compliant with the IEC-
60958 standard. It also supports programmable User Data and Channel
Status fields.

This IP is embedded in Microchip's sama7g5 SoC.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Link: https://lore.kernel.org/r/20200909145348.367033-2-codrin.ciubotariu@microchip.com


Signed-off-by: Mark Brown <broonie@kernel.org>