ASoC: sun4i-spdif: Add 24bit support

Merge series from codekipper@gmail.com:

I've tested this patch series on the Allwinner H3, A64, H6 and H313 SoCs
up to 192KHz.
24bit support is working on my H313 board but 16bit plays a bit slow and
I suspect that there is an issue with the clock setups. This is even
present without this patch stack. I would look to address this asap,
but for now can you please review what's here.