ASoC: wcd9xxx: maintain micbias for headsets have threshold on mic

There are headsets that require to maintain  micbias while it's plugged
since mic of headsets have threshold to turn on mic.
Maintain micbias when this type of headset is detected in order to detect
headset button press.

CRs-fixed: 471512
Change-Id: If3caab97fe5187c91753756482ba425a3ba14118
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>