ASoC: rockchip: add support for i2s-tdm controller

This commit adds support for the rockchip i2s-tdm controller,
which enables audio output on the following rockchip SoCs:
- px30
- rk1808
- rk3308
- rk3566
- rk3568
- rv1126

This is a cleaned up version of the downstream vendor kernel's
driver. It can be enabled through the SND_SOC_ROCKCHIP_I2S_TDM
configuration option.

Signed-off-by: Nicolas Frattaroli <frattaroli.nicolas@gmail.com>
Link: https://lore.kernel.org/r/20211001171531.178775-2-frattaroli.nicolas@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>