ASoC: TWL4030: Add DAPM event handler for output MUX selection

ASoC: TWL4030: Add DAPM event handler for output MUX selection

DAPM event handler is set to filter out invalid MUX settings
for certain outputs.
Earpiece:
 - 0 = Off
 - 1 = DACL1
 - 2 = DACL2
 - 3 = *** Invalid ***
 - 4 = DACR1

PreDriveL/R:
 - 0 = Off/Off
 - 1 = DACL1/DACR1
 - 2 = DACL2/DACR2
 - 3 = *** Invalid/Invalid ***
 - 4 = DACR2/DACL2

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>