ASoC: audio_graph_card2: Support variable slot widths

Merge series from Richard Fitzgerald <rf@opensource.cirrus.com>:

This adds support for I2S/TDM links where the slot width varies
depending on the sample width, in a way that cannot be guessed by
component hw_params().

A typical example is:

- 16-bit samples use 16-bit slots
- 24-bit samples use 32-bit slots

There is no way for a component hw_params() to deduce from the information
it is passed that 24-bit samples will be in 32-bit slots.

Some audio hardware cannot support a fixed slot width or a slot width
equal to the sample width in all cases. This is usually due either to
limitations of the audio serial port or system clocking restrictions.