asoc: codecs: wcd937x: Read and store mic bias value

Mic bias value is needed in case of special headset
detection logic and the same needs to be read and stored
from device tree to be used by mbhc driver.

Change-Id: I0b120b8bb130a4d101c97e118395a11e74c921af
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>