Add a couple of scripts to select the mic channel

[pierrechevalier83]

Analogous to the headset/speaker scripts. I got the specifics from here: https://chromium.googlesource.com/chromiumos/third_party/adhd/+/75c7236648d9ec78bb321f6a5484276d71600ee1/ucm-config/samus/bdw-rt5677/HiFi.conf

[raphael]

Great, thank you!