ASoC: TWL4030: Add EXTMUTE to reduce pop-noise effect

According to TRM, an external FET controlled by a 1.8V output signal
can be used to reduce the pop-noise heard when the audio amplifier is
switched on. It is suggested that GPIO6 of TWL4030 be used, but any
other gpio can be used instead. This is indicated in machine driver
with the following twl4030_setup_data members:

-hs_extmute. Set to 1 if board has support for EXTMUTE.

-set_hs_extmute. Set to a callback funcion to control an external gpio
line. Set to NULL if MUTE[GPIO6] pin is used.

Codec driver takes care of enabling and disabling this output during
the headset pop attenuation sequence.

Also add a delay to let VMID settle in ramp up sequence.

Signed-off-by: Jorge Eduardo Candelaria <x0107209@ti.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>