Add driver for the internal audio codec of the Rockchip RK3308 SoC.

Initially based on the vendor kernel driver [0], with lots of cleanups,
fixes, improvements, conversion to DAPM and removal of some features.

[0] https://github.com/rockchip-linux/kernel/blob/develop-4.19/sound/soc/codecs/rk3308_codec.cSigned-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://msgid.link/r/20240305-rk3308-audio-codec-v4-4-312acdbe628f@bootlin.comSigned-off-by: Mark Brown <broonie@kernel.org>