ASoC: ac97: Drop support for setting platform data via the CPU DAI

This has no users since commit f0fba2ad ("ASoC: multi-component - ASoC
Multi-Component Support") which was almost 5 years ago. Given that this runs
after CODEC probe functions have been run it also doesn't seem to be that
useful.

So drop it altogether to make the code simpler.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>