ASoC: wcd: Add support for MBHC ADC on WCD9340 codec

MBHC(Multi Button Headset Controller)
ADC(Analog to Digital conversion) method is used
for plug type detection. Add support for MBHC ADC on
WCD9340 codec.

Change-Id: I07d98ec8a4096dfd050535e382db7deca3d23d9b
Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>