ASoC: remove codec reg_cache

Codec reg_cache is legacy feature, almost all driver are now using
common regmap, and very few driver had been used this legacy feature.
Because of this background, it is now implemented on each
driver internally now.
So now, no one is using codec reg_cache. Let's remove it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>