RK3576 SPDIFRX

The RK3576 includes support for receiving SPDIF signals. This hardware is different from the SPDIF transceiver hardware on the RK3568 et al, and is apparently compatible with the RK3308 SPDIF receiver (which also has no mainline driver).

A binding and a driver for this new IP is missing from mainline, as well as the DTS nodes in the RK3576 SoC dtsi.

Vendor driver code: rockchip_spdifrx.c rockchip_spdifrx.h

Chapter 27 in RK3576 TRM Part 1.

• Identify where the boards we have access to may have an SPDIFRX pin accessible, devise a test setup (@fratti has some basic SPDIF/TOSLink hardware and can jank together something probably)
• Port and clean up vendor driver
• Add the device tree nodes to the RK3576 SoC .dtsi
• Write a binding