ucm2: Improve devkit config

Use the mux to switch mics and properly configure defaults.
3 jobs for devkit-ucm in 3 minutes and 37 seconds
Status Job ID Name Coverage
  Package
passed #328004
librem5
package:deb-debian

00:00:35

 
  Test Package
passed #328005
librem5
autopkgtest-debian-package

00:03:02

passed #328006
librem5
lintian-debian-package

00:00:29