ASoC: add additional controls to the CS4270 codec driver

ASoC: add additional controls to the CS4270 codec driver

Update the CS4270 codec driver to allow applications to use the mixer to
control Digital Loopback, Soft Ramp, Zero Cross, Popguard, and Auto-Mute.
Soft Ramp, Zero Cross, and Auto-Mute are disabled by the driver when it first
initializes the hardware, but these features either don't work or interfere
with normal ALSA behavior.  However, they can now be re-enabled by an
application if desired.

Remove CONFIG_SND_SOC_CS4270_HWMUTE and always allow ASoC to control the mute
bits.  The driver previously and erroneously assumed that these bits
control only external muting circuitry, but they also control internal
muting circuitry, so they should always be used.

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