ASoC: remove stand-alone mode support from CS4270 codec driver

The CS4270 supports stand-alone mode, where the codec is not connect to the
I2C or SPI buses.  Instead, input voltages configure the codec at power-on.
The CS4270 ASoC device driver has partial support for this mode, but the
code was never tested, and partial support doesn't help anyone.  It also made
the rest of the code more complicated than necessary.

[Removed redundant CS4270 dependency on I2C -- broonie]

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>