ASoC: wcd9xxx: Add config variable to enable/disable impedance detection

Some of the codecs still do not support impedance detection feature.
Currently it is only enabled for wcd9320. So, add a config variable
to mbhc configuration to enable or disable impedance detection
calculation.

Change-Id: I2d32d4f3bbdcd6211accf1278dd5ab44d6520b6e
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>