ASoC: mchp-spdifrx: add driver for SPDIF RX

The new SPDIF RX 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/20201002160305.815523-3-codrin.ciubotariu@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>