ASoC: twl4030: Remove local reg cache

Depend on the regmap reg cache implementation for register caching done in
the twl-core driver.
The local register cache can be removed and we can keep only shadow copies
of certain ctl registers for pop noise reduction.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>