ASoC: alc5623: Convert to direct regmap API usage

Convert to directly use the regmap API, allowing us to eliminate the last
user of the ASoC level I/O implementations (there are still open coded
I/O implementations in drivers), avoiding duplicating code in regmap.

We no longer cache the entire CODEC register map on probe since the more
advanced cache infrastructure in regmap is able to fill the cache on
demand.

Signed-off-by: Mark Brown <broonie@linaro.org>