ASoC: wcd9xxx: Maintain micbias for headsets with 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: 587697
Change-Id: Ie2bc622d4336ab9b772cd996db84b569dacd9bf6
Signed-off-by: Simmi Pateriya <simmip@codeaurora.org>