Continue refactoring the microphone detect handling by factoring
out the handling for microphone detection and button detection
into separate functions. This both makes the code a little clearer
and prepares for some planned future refactoring to make the state
handling in the driver more explicit.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>