configs: add initial value for "ADC2 Volume"

Initial value for this mixer ctl is missed, this is
to fix an issue that, when VA session on headset mic
is disabled, it can be reset to 0 and causes low
volume for audio recording.
Also, valid volume range is from 0 to 20, assign
a valid value for it.

Change-Id: Ia6b71a09b3b7f4b7918caed5499e606e861a44d7
12 files changed