ASoC: cs4270: use the built-in register cache support

Update the CS4270 driver to use ASoC's internal codec register cache feature.
This change allows ASoC to perform the low-level I2C operations necessary to
read the register cache.  Support is also added for initializing the register
cache with an array of known power-on default values.

The CS4270 driver was handling the register cache itself, but somwhere along
the conversion to multi-compaonent, this feature broke.

Signed-off-by: Timur Tabi <timur@freescale.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>